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FAQs About Water Evaporation, Make-Up H20: Water Quality/Adjustment

Related Articles: Marine Water Change, Captive Seawater Quality, General  Marine Maintenance

Related FAQs: Make-up Water 1, Water Changes for Marine Systems 1, Make-up Water: Rationale/Use, Gear, Frequency/Amount, Techniques, Trouble/shooting, & Top-Off System s, Controllers, Treating Tapwater Marine Water QualityMarine Plumbing


simple question, hopefully a simple answer?     4/22/12
Hi WETWEB guys AND girls!!!!
<Hi Again Pam, Bobby here>
With what do you raise the alkalinity AND pH of top off water to a reef tank?

<You do not need, nor want, to adjust either of these for top off water.>
Now, I'm holding my breath, cause I'm adding water now !
<Breathe and add water>
Thanks everyone for your expert advise!
<You are welcome, Bobby>
Re: simple question, hopefully a simple answer? ATO water qual.      4/23/12

REALLY!!!!!!!!!!!! ???????????
That's surprising because when "making"  the water (RO) these are the results;
 a.. 10ppm nitrates
 b.. Alk 40 !
 c.. pH 6.8 !
You're saying this is fine to use and won't disrupt my already slow to balance system?
<PH looks fine, I am not sure what you mean by Alk of 40, unless  you mean 4.0 meq/L (please clarify), and you should not have that much Nitrate in RO water.  So, are you using DI also after the RO membrane?  Have you tested the TDS coming out of the unit?  What are you storing the new water in? 
Again, please clarify these things.>
I also want to sent out a big apology for using this easy way out to find answers.
Yes, I do go to WETWEB to read, but find it difficult to sift through the many, many letters it receives. You know how it is, it's like when you Google a subject and get 100k hits.
So, just to let you know, that I think of you guys and how you must put up with redundant and I'm sure sometimes "daaaah" questions.
I can hear you all saying ....."gee people,............ read a book!"
So with that said, I will do my best to call on you ONLY when on the verge of a nervous breakdown!
Cheers to you all!

Top Off Water Buffer 8/17/11
<Hello Barry>
I have my RO/DI top off water in a 35 gallon container. From there it travels through my PM Kalkwasser reactor then into my sump. Do I need to add buffer to this 35 gallon container of ro di water or will it interfere with the calcium hydroxide.
<Only if your tank water parameters dictate so. It shouldn't cause a reaction with the hydroxide as long as the buffer is well mixed before going into the reactor.
James (Salty Dog)>

RO/DI Top Off Water 11/4/09
Hello Guys!
<Hi Roger>
Now running a 125 gal FOWLR/LS. I'm using a 90 GPD Spectrapure RO/DI unit for my "top off" and saltwater changes.
Read a lot about preparation prior to adding salt but what do I need to do with this low pH/Alk water for daily top offs?
I've taken notes, please tell me if this is correct !!!
1 - aerate for 12-24 hrs.
<Not necessary with RO/DI water.>
2 - Add sea buffer, is there a difference between Aquarium Systems vs. CaribSea?
<I do not readily know the make up of these two, but my choice would be Seachem and/or Tropic Marin products.>
Add appropriate amount to buffer to 8.0?
<I would shoot for something closer to 8.2..>
Aerate for an additional 24 hrs.
<Using a powerhead to mix the buffer will be fine.>
This freshwater can now be used for my "top off" needs?
<Yes, and I would keep the RO/DI water temperature close to what your system temperature is.>
3 - Later, add salt for regular water changes.
<Yes. You may want to read articles/FAQ's here.
Thank you so very much.
<You're welcome. James (Salty Dog)>
RJS - Retired Salmon Biologist

Maintaining dKH using buffers in ATO: Chasing numbers. SW Alk\pH\Ca balancing 8/6/2009
Hello Crew,
<Hi Mark.>
I'm jumping over here from the WWM Forum to maybe get an answer to my question and a potential solution. You have been tremendously helpful in the past and I appreciate the service you provide. I've read through much of the discussions on PH, alkalinity, and calcium at WWM and I believe I have a fairly good understanding of it.
<So you understand that as Ca rises, Alk will fall, and as a general rule of thumb, Mg should be 3x the Ca levels.>
However, after implementing what I thought would be a relatively easy way to keep my system alkalinity stable, I find myself with a small problem that I can't seem to figure out. I'm having a problem keeping my dKH stable without adding buffers to the tank. I want to be able to keep it buffered with the ATO water.
I measure my dKH regularly and I'm having trouble maintaining anything above 8 and it occasionally falls to 7 dKH.
<Which is fine actually.>
I can, with additives, get the dKH higher than 8, but it seems to want to fall back to 8 or less
even with massive amounts of buffer in the ATO water.
<So why keep fighting it?>
What is confusing to me is that I took readings this morning and my tank was at 7dKH. I
checked my premixed salt water and it's at 8dKH.
<No biological activity in the premix to bring it down.>
I checked my FW ATO tub and it's at 21dKH.
<Wow, How much are you buffering?.>
I use Sea Chem powdered products (Reef Buffer & Reef Builder) in my ATO water to buffer the tank, but I never really know how much to add or how high I need the dKH to be to keep the tank alkalinity up.
<A dKH of 6 - 12 is fine, provided it is stable.. Remember, stability is more important that a set number.>
I perform weekly 10 gallon water changes. I recently changed from Reef Crystals to SeaChem Reef Salt and that seems to be helping a small Cyano battle I've been wagering for the last year. I just couldn't completely knock the stuff out, so I changed salts to see if it helped.
It seems to be helping. The Cyano is retreating again, not that there was massive amounts of it....but it's ugly. The LR rock looks noticeable better too after only 4 weeks.
<A good sign. You don't mention what else is in the tank though..>
What I do not understand is how the dKH can be so high in the ATO water and it seems to be doing nothing to keep the tank dKH level from dropping.
<The buffers are being used\ 'burned' up or precipitating out of solution.>
My ATO uses about 1.5 gallons per day. This has been an ongoing issue since I set the system up. I'd be happy to keep the dKH stable at 8 or 9, but I don't seem to be able to do that without adding buffer directly to the tank occasionally. All of my RO/DI water is aerated for several days before use.
The only thought I've had is that I need to start buffering my premixed salt water to a higher dKH as well as the ATO water.
<A dKH of 8 is fine for premixed water.>
Readings taken last night:
PH: between 8.0 and 8.5 (hard to read between the scale)
<How much does it swing between lights on and lights off?>
dKH: 8 (added reef Builder in the morning, was dKH 7)
<If you don't add anything, what does it drop to?>
Calcium: 375 (time to add some Reef Complete)
<What is your calcium demand over a period of time?>
Magnesium: 1410
Phosphate: undetectable
Nitrate: 0
Tank: setup in April of 2008
90 gallon reef tank
30 gal DIY sump with integral refugium..7-8 gallon (Aragonite DSB and macro Algae)
1.5" drain
MAG 7 return pump
1/2" of sugar fine Aragonite substrate
<All fine. Do you use reverse lighting on your refugium?>
Aqua C EV-120 running on a MAG 5
50-60lbs of Live Rock
MAG 18 on Closed Loop for added circulation
(2) 150W 10K HQI's
(2) 55W Actinic
(1) 55W 10K Power Compact over refugium for macro growth
Support Eq:
Typhoon III 150 gallon per day RO/DI unit
15 gallon container with Buffered RO/DI water and Tunze ATO unit
29 Gallon tank for premixed salt water
<All good.>
<I think you are caught in a trap many of us get wrapped up in: Chasing numbers. The 'book' or specification states that dKH should be X and Ca should be Y so we add buffers and chemicals, and dose this and that and wind up chasing our tails.>
<What you need to do here is stop. Other than salt, and enough buffer in your top off water to get a pH of 8.2 - 8.4 and a dKH of about 7 - 8, stop adding chemicals to your system. Then, measure your dKH, pH and Ca both morning and night for a few days. record your readings. If your dKH drops below 6, add just enough buffer to bring it back. You should know what your calcium demand is, ad well as what your dKH wants to naturally rest at.. The key thing to realize is, if your Alk wants to stay at 7, let it.
Stability is much more important than chasing that perfect number.>
Thanks Again
<My pleasure, will also be posting this on the forum.>

Top off water and Testing for RO Water TDS 4/27/09
Bob and the Gang,
<Hello Joe>
Hope all is well.
My 135 G Reef tank loses a lot of water due to evaporation.
I add a fair amount of RO water to top it off weekly.
<Am I to understand you top off the tank once a week? Or do you mean you lose a lot of water over the course of a week. If you are topping off only once a week I suggest you try to do it more often, the longer you wait before topping off the tank, the larger the swings in the specific gravity of the water your tank will experience>
<There are auto top off devices available to top off the tank for you and provide a more consistent environment for your tank inhabitants. Search 'ATO' on the Google search box at the bottom of WetWebMedia.>
My question is, should I be adding something to my top off water? Never thought I had too, but I've read a
couple of places where they recommended adding something to keep the PH up.
<It is possible to buffer the water, but not necessary, assuming you are testing and adjusting alkalinity as needed. Just continue adding topping off your tank with RO water, pH swings will be less noticeable if top offs are done on a small consistent scale like with an ATO. You can also aerate your top off water to remove CO2 from it prior to use.>
Also, how can I be sure that my RO unit is working properly (I have the Coralife Pure-Flo)? Is there something I can use to test the RO water? I was reading about TDS testing but wasn't sure if that was necessary.
<I would highly recommend testing the Total Dissolved Solids from the effluent hose of your RO unit. Membranes do lose their potency over time from normal use, but this can be accelerated depending on what chemicals your city adds to the water. Testing TDS is one of the most simple ways of checking the quality of effluent coming from a RO unit, and basic TDS meters can be had at a very low cost.>
<Your welcome.

Re: Top off water and Testing for RO Water 4/27/09
Thanks Josh. Yes I'm topping off roughly every week. I usually lose close to 10 gallons a week! You make a good point about trying to do it more often to avoid larger swings in specific gravity. I'll definitely try to
do that.
I'll also look into a TDS tester.
Thanks again.
<Your welcome, I think you will come to enjoy not carrying full buckets of water around. Josh>

pH of top-off water  9/23/07 Good morning all, <Kim> As always, thank you so much for sharing your knowledge with all of us out here on the learning curve of this hobby. I have been struggling with maintaining the PH level of my top off water. I have attached the information that I have found on WWM below for reference/background, as this person had the exact same problem I am experiencing. <Okay> I keep about eight gallons of top off at a time right now. Recently I purchased a RO/DI unit, and at the same time I switched from using Kent Marine Buffer over to SeaChem Marine Buffer. Since then I have not been able to keep the PH up in the Top off water. After researching here, I thought that maybe the powerhead I have in the bucket is not strong enough. <Mmm, shouldn't matter> I upped it to a Maxijet 1200, and it hasn't helped at all. I aerate the water with the powerhead, and keep it heated as well. <Good> I also keep a cover on the bucket. If I buffer it to proper PH at night, the next day it is consistently back down below the PH scale. <May need to leave the top off...> Do you have any other suggestions as to what could be wrong? I'm wondering if the process works such that when you add the buffer and test an hour or so later, the test should be off the charts, but settle back the appropriate level the following day? <Usually so, yes> Presently I'm only adding enough buffer to bring it up to the 8.2ish range within an hour or so. As an aside, like the other inquirer, I live in an older home, so it is not super-well insulated. <Actually better most times for air exchange...> Thank you for your time. Regards, Kim in Boston <I would first try leaving the mixing container top ajar for a day... Next I would try adding a teaspoon or two per five gallons of simple baking soda (Sodium Bicarbonate) to see if this moves the pH. Please do re-contact me/us re. Bob Fenner>

Fresh water top offs... SW chem. confusion, not reading...   8/2/07 Hello Bob & Co, My water PH is 8.0. 1. Is it wise to bring the PH of the fresh water I use to compensate for evaporation, to 8.0 by adding baking soda, before topping off? <Yes... but not with sodium or other bicarbonate... need carbonate, other material with higher kOH...> 2. If so, how many teaspoons per gallon of fresh water do I need to add, to raise it from 7 to 8? Cheers, Gans <Please read here: http://wetwebmedia.com/marphalk.htm and the linked files above. Bob Fenner>

Re: Water change - Top Off Strategy  8/27/05 Thanks for the quick response. A follow up if I may. <Sure> I got a new pH pen today and discovered my pH is 7.7. Not 8.1 like the test kit told me! KH is 9.5 and Calcium is 300. Tank is 90 gallons, 7 weeks old with a few soft corals and 3 small tank bred clowns. <Okay> My plan is to use SeaChem Marine Buffer 8.3 (1 teaspoon for 20 gallons) and add Seachem Kalkwasser (1 teaspoon per gallon) to my change water. I will then change 10% of the water per week and hope that the pH starts to climb with the water changes. <Sounds good> Is this reasonable or do I need to take more drastic measures to the tank right away. I am trying not to shock my fish as they all seem happy. <Mmm, no... nothing drastic... not many good things "happen" quickly with marine aquariums> Does the Kalkwasser dosage seem high or do you really need to add that much! <Mmm, depends on a few factors... bio-load mainly, but experimentation is key here... add some, test later...> Do I need to be careful not to siphon of any unused Kalk in the bottom of my water change bucket? <Mmm, no... Please read here: http://www.wetwebmedia.com/kalkh2ofaqs.htm and the linked files above> Sorry for all of the questions but this is very confusing. Thanks. Keith <Keep studying, contemplating... you'll be less confused... Bob Fenner>

Iodine use Hi I have constructed a 500 gallon system for cryptic filter feeders.   There is an algae scrubber and a skimmer.  I will be importing tunicates, sponges, Dendronephthya, file clams... water movement is via a fast current generated by a large water lift into the scrubber, and a Wave2K.  The system has three tanks and two refugia, so that I can isolate and experiment.      There is an automatic top off unit for RO water.  My question is- is there any problem (other than the controversies about using iodine at all)  with putting the iodine in the freshwater top off tank?
<< I don't think there is a problem, but I would probably dose into the tank. >>
 This would allow continuous infusion.  Also, if no problem, can I also add two part alkalinity/calcium supplement to the same reserve with no interactions (i.e. does iodine precipitate on calcium carbonate)?
<< Well you can't add the two parts of a two part solution together.  You could add buffer to your RO water, or add calcium, but you can't add both.  Soooo, I would suggest dosing iodine and calcium, and adding your buffer to your RO water.  I wouldn't mix calcium or iodine in, because you don't really know what reactions may take place. >> Thank you so much! Charles Matthews <<  Blundell  >>

Buffering Makeup Water WWM crew, <Hi there! Scott F. here today!> HI I'm new to your site but I have already found a wealth of helpful info. After extensive research of your RO water FAQs I still have a question about buffering fresh RO/DI water.  I hadn't been buffering my raw water, well until about a week ago,  anyway I tried to buffer with ESV ALK booster but the ph would go to 8.6 then slowly fall until it hit 7.2.  Not likening to add more chemicals than necessary I  decided to fill a filter bag with 2# of crushed coral and throw it into my makeup water holding tank. Now the ph stays at 8.0. OK now for question.  Is this an acceptable way to buffer my makeup water? I also have a power head circulating and aerating the tank. THANKS FOR SUCH A GREAT SITE, AARON SCHOTT <Well, Aaron, if it is working for you, why not keep it up! As long as you are using material that is not leaching phosphates or other nasty impurities, I don't see any harm in this practice, myself!>

Treating RO/DI water? 2/13/04 Anthony--I lose a quart a day, that I need to top off. Should I use buffered top off water, or just straight rodi water for a couple of days, since I added to much of SeaChem's buffer already.   Thanks Charlie <its fairly risky my friend. Its a better habit/solution to dilute a chemical imbalance with a water change (as other manipulations of chemistry may have occurred) and then resume with properly aerated and buffered seawater or fresh water for top off. Under almost no circumstance should you use raw, unaerated and/or unbuffered RO/DI/Distilled water for SW aquariums. Too unstable. Anthony>

Buffer Question <2/1/04) Hi Bob, <Steve Allen covering tonight.> I was wondering about the use of "buffer" additives to the RO water used to replace evaporation from my reef tank. Currently I do not add any buffer materials, but I am considering whether it would be wise to do so. My understanding is evaporation with remove 'n' number of H2O molecules (i.e., pure water evaporates); thus we have lost 2'n' hydrogen atoms. Therefore the top-up water needed to replace this should also be 2n hydrogen atoms, to ensure the effect on System pH is identical. Is my understanding correct? <Merely incomplete. You are not considering the factors that affect free H+ ions. True, pH measures these, but it is buffer that keeps them bound up so the pH stays alkaline in seawater. Otherwise, the tendency is to head to neutral (7.4), or even lower due to organic acids in animal waste. By performing RO on your tapwater, you have removed all of it's buffer capacity. Marine tanks naturally lose buffering capacity (carbonate hardness) over time, requiring replacement. There's a lot of good info available on this subject both at WWM and other web sources such as Advanced Aquarist Online.> If so, does this suggest top-up water should not contain buffer additives? <no> Or is it the case that marine tank pH tends to drift downwards due to the bio-load <yes>, and we are simply using the top-up water as a convenient mechanism to replace hydrogen lost due to the filtration of the System? <Not hydrogen lost. Buffer capacity to keep the H+ ions bound up and maintain the alkaline pH we need.> The reason I ask this question is that my reef tank starts the day at pH7.9 and ends at 8.1. <A reef ought to be kept higher. At or around 8.2 to 8.3 would be better. It would be nice to not have the pH drop below 8.0-8.1. I monitor mine electronically, and it never goes less that 8.1 or higher than 8.3> I am starting to benefit from a newly established reverse lit refugium with a DSB - hopefully my pH will continue to improve as the refugium matures. <Yes, this can help stabilize pH if you have macroalgae in it.> Besides weekly 8% water changes the only "additive" to my system is a calcium reactor. <Also great for replacing buffer.> I try to do without additives as they can prove costly over time, mistakes can be made with application (we are all only human!) and leaving the System to go on holiday becomes a larger burden for the person who looks after the tank. <For those who can afford the initial investment, this is a great way to go. Anthony is big on Kalkwasser. I use the 2-part buffer/calcium from B-Ionic, but the cost of that adds up over time. Someday I'll figure out where to fit a calcium reactor in my system.> If adding a buffer to top-up is the "done thing" in the industry then I will follow suit, but reading through the WWM pages left me uncertain if there was consensus in this area. <No absolute consensus out there.> What is your take on this subject? <IMO, the bottom line here is that you are replenishing the buffer in the tank with your calcium reactor. The reason to buffer your RO water is to replenish its own buffering capacity that was removed by the RO process. I have been very satisfied simply adding the recommended per-gallon dose to my RO water only when making new salt water for water changes. My water is so hard here that I do not seem to need to add buffer to my top-off RO (no DI), which has a pH of 8.8. I'd suggest you check the pH of your top-off. If it is in the pH range you need, then you don't need to buffer it.> As always, thank you very much for your advice. Andrew Senior <Hope this helps. I do not profess to be a chemist. Do read more if you desire a deeper understanding. Here's a start: http://advancedaquarist.com/issues/may2002/chem.htm >

- DIY Dosing Question - Hey guys :)  I made a DIY drip unit for my top-off water, which will be distilled water buffered to the proper KH.  My question is this-Can I dose Iodine with the buffered water? <I wouldn't.> Can I add gluconate CA to it as well? <You could, but I wouldn't.> I'm no chemist, and don't claim to know anything about it, but it seems as though these could be dripped together in one unit. <They 'could', but I wouldn't - I'd stick with the standard bearers - Kalkwasser or just clean water for top off. As for the iodine - I just wouldn't add this without testing. Gluconate+calcium is not the optimum way to get calcium into your tank, and then leaves you with all those sugars... look out problem algae. So no... I wouldn't bother topping off with either of those.> Thanks guys, you rock. <Cheers, J -- >

-Top-off water questions- Hey Kevin, Mike again, the leaves are starting to change color here in Edmonton so you know that "Winter is a comin". < :( One or two doing that around here too...>I am re-reading and re-reading over articles and FAQ about water changes since this is the number one thing a person can do to provide a good home for the little guys. I was rereading for about the 10th time this article http://www.wetwebmedia.com/water.htm and I am wondering. Do I need to buffer my tap water for water changes to get the pH to be the same as the tank, Target a pH of 8.2-8.6? or do I just have to be concerned about similar temperature, specific gravity and treat to remove chlorine/chloramine? <That would depend on what your test kit reads after you fully salt and aerate the water overnight. Every salt creates a slightly (sometimes not so slightly!) different batch of seawater.> If so/In addition,  baking soda can be used to raise Ph. how much would I use to prepare 5 gallons of pre-mixed water for water changes? <Check the carbonate hardness and pH before toying around with any additives, the salt should contain all you need.> and would you recommend this method? Thanks again Kev. <Good luck, don't forget to break out the long underwear! -Kevin> Cheers. Mike Tol

Water Treatment I have just found this site and I am grateful for the archives in Q&A type format. Thanks for all the great info. <Thank you for the kind words! We enjoy bringing it to you! Scott F. with you today!> I live in the United Arab Emirates, in an apartment, with limited space. It would be very handy for me to use bottled water (5 gal. water cooler style) from a local supplier. I have obtained a water quality report (see below). They claim that the water undergoes a RO process. Would you suggest that I buy an additional unit (something cheap and portable like the product shown here --> http://www.drsfostersmith.com/product/prod_Display.cfm?siteid=6  http://www.drsfostersmith.com/product/prod_Display.cfm?siteid=6&pCatId=4484&pCatId=4484   and put the water through another processing for my new marine tank under construction that will house fish and possibly some corals? Would the fact that I plan on regular water changes impact this decision? Thanks. Water Product Specification * pH  @ 25 degrees C = 7.8 8.2 * Conductivity @ 25 degrees C (|uS/cm)  =  95 - 105 * TDS @ 25 degrees C (mg/l)  = 95 - 105 * Total Hardness as CaCo3 (mg/l) =  35 - 45 * Total Alkalinity to pH 4.4 (mg/l) =  45 - 55 * Calcium (mg/l) = 15-20 * Magnesium (mg/l) =  03 - 05 * Sodium (mg/l) =  25 - 35 * Potassium (mg/l) =  0.5 - 0.7 * Bicarbonate (mg/l) =  55 - 65 * Chloride (mg/l) =  20 - 30 * Sulphate (mg/l) =  05 - 10 * Fluoride (mg/l)  =  0.45 - 0.55 * Total & free Chlorine (mg/l)  =  Nil * Turbidity (NTU) =  Nil * Taste & Odor  = Acceptable/Good Carolyn Munson <Well, Carolyn- your water looks to be pretty good, however, I'd highly recommend further treatment via an RO/DI unit. This is the best way to obtain consistent, high quality water. Hope this helps! Regards, Scott F>

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