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FAQs on pH, Alkalinity, Acidity: Measure

Related Articles: pH, alkalinity, In praise of hard water; How hard, alkaline water can be a blessing in disguise by Neale Monks, Treating Tap Water, A practical approach to freshwater aquarium water chemistry by Neale Monks, The Soft Water Aquarium: Risks and Benefits by Neale Monks, Freshwater Maintenance, Treating Tap water for Aquarium Use

Related FAQs: pH, Alkalinity, Acidity 1, pH, Alkalinity, Acidity 2, pH, Alkalinity 3, pH, Alkalinity 4 & FAQs on: FW pH/Alkalinity Science, pH/Alkalinity Adjustment, pH/Alkalinity Products, pH/Alkalinity Anomalies/Fixing, & Water Hardness, Freshwater Aquarium Water Quality, Treating Tap Water for Aquarium Use, Freshwater Algae Control, Algae Control, Foods, Feeding, Aquatic Nutrition, Disease

Update: Sediment/pH/Soft Water Issues      12/13/16
Greetings Neale, Bob, Crew!
First things first, a dead link in the box marked "Units please!" on this page : http://www.wetwebmedia.com/alkmeas.htm
And here's a conversion calculator I found:

re: New rainbow fish won't eat; How do I measure alkalinity?       10/1/19
Hi Neale thanks for your reply
How do I measure alkalinity? Because I was buffering ph and kh? Yet the product mentions alkalinity a lot
<For freshwater systems, alkalinity and carbonate hardness are essentially interchangeable. Alkalinity is technically the ability of water to resist acidification, but in freshwater tanks, most of this capacity is down to carbonate hardness. Hence, no need to fuss over the difference. Low KH will likely be low alkalinity, and vice versa. Cheers, Neale.>
re: New rainbow fish won't eat; How do I measure alkalinity?       10/1/19
Hi again Neale Thanks for your reply.
I have just been working out keeping the other container with snails clean and doing some water changes on the main tank to remove the meds. Also added seachem Purigen. I was reading those 2 products and it seems the former has a lot more potassium than the later one. So yeah I will get the alkalinity one. The kh in my tank is 2-3 what am I aiming for? It seems pretty close to the tap water.
<Most New Guinean Rainbowfish are happy around 5-10 degrees KH, alongside moderate general hardness (5-15 degrees dH). So long as the pH is steady around 7.5, and the KH is at least 5, the water is probably fine, and won't need any further diddling around with. Cheers, Neale.>

tapwater readings... anomalous for tap/China, Neotrop. Cichlid use     5/24/13
Hi Crew.
I've moved recently, and am a bit confused by current tapwater readings: pH 8.7-8.8
<Whoa, high! Though ours here in San Diego is generally 8.2-8.4>

 (electronically measured but drip test gives similar readings of pH8-9), KH 0-1, GH 0-3. Not sure if it matters, but I live in China, and I have no idea what chemicals/processes are used to treat the tapwater.
<Strange... something not registering (much) as general or carbonate hardness... I'd use a standardized solution or two to check you meter>
If I store the water for one or more days pH remains stable and does not decrease. If I add baking soda pH seems to go up and then come down to basically the same level as the tapwater, i.e. around 8.7-8.8.
Currently I add Epsom salts and baking soda, to increase KH and GH, while aerating the water for a minimum of 24 hours, and I add Seachem Prime to the stored water just before I make the water change.
I've tried SeachemMarine Buffer hoping this would stabilize pH around 8.3 but instead pH exceeds 9 after addition of this product.
<Mmm, yes>
I am keeping Central American Cichlids (Nicaragua Cichlids and Thorichthys Maculipinnis) so it's not that I need to get my pH down to 7 or so...but still, I am not sure if a steady pH of 8.8 isn't a bit over the top here.
<Could well be... I'd get/use a reverse osmosis device to mix water for your neotropical Cichlids and your potable uses>
Is a steady pH of 8.8 acceptable for these fish?
<Too high>
 Is there any (simple) way I can increase hardness and lower pH?
<Not as far as I'm aware. There is something anomalous here... You need to check your checkers... and look into RO>
Henk Naert
<Welcome. Bob Fenner>
Re: tapwater readings; parsimony rules      5/24/13

Hello Bob,
Thanks for your speedy response. Just wanted to let you know that indeed the simplest explanation (unfortunately often overlooked) is most often correct. Just put a spare Tetra test kit to use, and my tap water tests 7.5 out of the faucet (will test again tomorrow after aerating 24 hours),
 tank water tests at 8 (which I assume seems to be correct considering I add baking soda to the water I prepare for water changes). Tap water currently KH1, GH4; tank water KH4, GH8. I assume these values make more sense.
 Would you further increase KH and GH or is it fine as it is now ?
<Mmm, I'd leave as is... and make substantial water changes weekly... a third of volume perhaps... vacuuming the bottom>
(I have been a bit conservative adding baking soda and Epsom salts not understanding very well what was off with the pH value). I guess electronic meter needs to be recalibrated or is not functioning properly.
<Quite common>
Thanks for your help!
Henk Naert 
<Thank you, BobF>

conversions and equations, FW hardness, nay SW Alk       3/5/12
Can someone please send me the math equation to convert 125KH to ?
<125 degrees KH is a very unlikely number! Do you mean 125 mg/l calcium carbonate?>
In other words, if .......... 8 dKH = 143.2 mg/L ........... then my reading of 125.3 kH = ?
<It's very simple. There is 17.8 mg/l calcium carbonate per 1 degree KH. So 178 mg/l would be 10 degrees KH. 125 mg/l would be 125/17.8 = 7 degrees KH.
Some test kits will also use 17.8 mg/l calcium carbonate per 1 degree dH, but strictly speaking, 1 degree dH should be 10 mg/l calcium oxide. Do read:
It's honestly not difficult provided you understand degrees dH applies to general hardness and degrees KH to carbonate hardness (and that these two things aren't identical).>
I know you all have probably been through this way too many times!
I've been sitting for the last 15 minutes, with 3 tabs open,  looking for this conversion. No luck!
If there was a way to do a fine tuned search at WetWeb, ( Boolean?) you would more than likely have less mass questions!
Thanks so much!
<Cheers, Neale.>
Re: conversions and equations

<Who's Dean?>
Oh, very sorry about the caps!
<Real good. Cheers, Neale.>
Re: conversions and equations

LOL!!!!!!!!!!!!!  Where did I get DEAN?????????
NEALE!!!!!! So sorry again!!!
<No probs. Neale.>
Re: conversions and equations

I have a salt water tank,...not fresh! Hopefully the link you sent goes for Reef tanks as well??
<Yes. But reef aquarists normally focus on alkalinity, which is slightly different:
Rather than carbonate hardness alone, they're worried about the ability of seawater to resist pH changes and also to provide the calcium carbonate corals and suchlike need.>
Ok, really leaving you now!
<Cheers, Neale.>
Re: conversions and equations      3/5/12

Thank you for the new link. Reading now!
<Cool. Cheers, Neale.>

pH and water flow  5/17/07 Crew, <<Hi, Erik. Tom with you.>> Great site, thank-you. <<Thanks, Erik. Glad to hear we've been helpful so far.>> I have a 30 gallon tank with Eco-Complete as substrate and nothing else in it. I use RO/DI water. My Pinpoint pH monitor reads the pH as 7.2 and up with the Whisper 40 running (only has carbon in it) and reads 6.75 and lower with the filter off and not flowing at all. Why? <<Well, now both of us have an issue to deal with. Your issue is that pH monitors don't work well in purified (RO/DI) water. Mine is trying to explain, in simple (?) terms, why they don't. First, and not surprisingly, RO/DI water has very little in the way of buffering capacity which means that pH can change quite readily, up or down. Simple enough. Second, commonly our pH is affected by the absorption of CO2 from the atmosphere. This is why you can expect pH to typically decrease over time since dissolved CO2 in the tank lowers pH. How quickly this takes place depends on a wide number of factors but, once again, this can depend, in part, on the buffering capacity of the water. In our homes, CO2 levels can be, and typically are, higher than outdoors yielding a higher concentration of the compound in the air and, therefore, greater opportunity for our tanks to absorb it. (RO/DI water generally runs in the pH range of about 5-7 depending substantially on the level of dissolved CO2.) Third, CO2 is 'driven' out of the water by agitation such as what you might create with airstones, UGF's, HOB filters, etc. Though this doesn't even scratch the surface of a highly complex topic, I believe that what you're seeing is the absorption/dissolution of CO2 in your tank caused by calm periods (filter off) resulting in increased CO2 absorption (lower pH) followed by active periods (filter on) resulting in decreased CO2 (higher pH).>> Also, the readings on the pinpoint monitor fluctuate a tenth of a point constantly, it is never pegged. I know constant pH is better than a specific reading and I can't get the pH to stay at one reading even in this small tank. <<The greater the precision of the instrument, the more likely it will be to show variances, Erik. You might think of it like the 'refresh rate' of your computer monitor. The higher the refresh rate, the more screen 'flicker' you'll observe. Your Pinpoint monitor is constantly refreshing its readings. In conjunction with what I've already discussed, I'd be very surprised if it weren't constantly fluctuating. A very nice piece of gear but it has drawbacks in this particular set of circumstances.>> Respectfully, Erik <<Hopefully this will shed a little light on your situation, Erik. Best regards. Tom>>

pH mystery-please help!! -- 06/27/07 Hi crew. Thanks for answering my previous questions regarding tank setup and stocking levels. I have a new question that has me completely baffled. I am completely stumped as to why my pH is sooo low. <The tendency for all aquaria is to become acidic over time. What inhibits this is the buffering capacity of water (specifically, its carbonate and bicarbonate hardness) and the frequency of water changes. The simplest approach to declining pH is to just change more water, more often, assuming of course that your tap (faucet) water has a higher pH.> I have a 55 gallon discus aquarium that is home to 8 discus (3-5") and a relatively large Anubias barteri. Other plants have not faired well and were removed. <Anubias is the Aspidistra of the aquarium plant world. I inherited a specimen that lived for TWO years in a tank with no lights!> Present tank configuration is over a year old now. <So should be stable.> Recently, the pH reading on my Milwaukee SMS122 monitor took a dive. Water changes did not move the pH, so I was convinced that the probe failed (again). <Certainly possible. But also check calibration and good old fashioned user error. There's often an argument for using a simpler, if less accurate, test kit that delivers consistent results.> I replaced it, but when I installed the new probe (after calibration) I was shocked to find that the pH reading was the same: 3.9!!! <Dead fish would be here. Remember, the pH scale is logarithmic, i.e. pH 5 is 10 times more acidic than pH 6, pH 4 is 100 times more acidic than pH 6, and so on.> I manually tested the water parameters, but the test kit that I have tests only down to pH 6. Of course, the water tested at the bottom of the pH scale. <It is entirely possible for regular aquaria to dip below pH 6 to around 5.5 under certain circumstances. Usually, you'll notice plants wilting and snails heading for the surface of the tank. The fish will usually behave in obviously odd manners as well. Much below 5.0, and most fish will simply die. There are some acidophile fishes, such as Hemirhamphodon pogonognathus that enjoy such conditions, but the vast majority do not, Discus included.> Nitrates were 10ppm (I know, it is time for a water change!) Ammonia was 0.25ppm, and no nitrites. <The ammonia is lethal at this level. I'm staggered your Discus are alive, to be honest.> Water changes are done with R/O water. <Ah, what are you mixing the RO water with? You do need *some* hard water in there. Around 3 parts RO water to 1 part hard water (~ 20 dH) gets you water at ~5 dH which is about right for Discus. This gives the water at least some buffering capacity, enough to last between weekly or twice weekly water changes. Pure RO water has ZERO buffering capacity, and the simple background acidification will rapidly drop the pH. It isn't even safe to keep fish in pure RO water. Although the science is fuzzy about this, fish do seem to absorb some minerals from the water they drink.> Do I need to do a really massive water change to move the pH back up, or add some treated tap water? <You shouldn't ever *need* to do more than 50% water changes a week. Doing more water changes is a good idea, but if they're *essential* to keeping the aquarium stable, then something is amiss.> I don't know about the chemistry of my tap water. I stopped mixing it in due to a terrible algae problem that I ended up resolving be completely breaking the tank down and cleaning it (before I got the discus). <Non sequitur. Tap water doesn't cause algae. At the very least, you want to be adding maybe a 10-20% dose of Malawi or Tanganyikan salts to the water to get some background hardness. You're aiming for a pH around 6 and a hardness between 5-10 dH. There is absolutely no advantage to keeping the pH and hardness below this level, especially if you're having pH problems. Plants HATE very soft water, and that may be one of your problems. Most aquarium plants want a neutral pH and low to moderate hardness. Assuming lighting and CO2 are adequate, this may be a key problem for you. Once you have thriving plants, algae pretty much goes away by itself, almost regardless of background levels of nitrate and phosphate. It sounds simple, but it's actually true.> OR, is it time to break the tank down again and clean??? <No. Review what you're doing in terms of mixing RO water with hard water: I'm 99% sure that's the source of your problems.> This is really freaking me out and I don't know what to do!!! The fish must be acclimated to it-they are eating and behaving normally as far as I can tell. <Yes, fish can acclimate to surprising things. I've heard of marine fish (sweetlips to be precise) being kept in outdoor pools that were so low in salt that freshwater plants were growing. But still, the idea is to try and create stable conditions, because in the long run that's what most fish like best. The precise pH and hardness values are secondary in importance compared with actually keeping them steady over time.> Bad timing (or maybe not) for this problem to arise. I am in the process of researching what I need to upgrade to a 90 gallon tank. I will supplement filtration with a HOT BioWheel type filter, maybe an Emperor 400. <The filter is probably a good idea for an upgrade, given the background ammonia level, but -- below pH 6.0, biological filtration slows down dramatically, and it stops once you reach pH 5.0. Another good reason to keep the pH at 6.0.> ANY help will be gratefully received!! Thank you very much. <Hope this helps, Neale>

Re: Accurate Test Kits ? I did check the dates and they are fine the kit I was using for nitrates expires 2007. I have never heard of LaMotte kits. I had to go to 4 stores to find Tetra Test kits. It was either that or the strip kind of tests. Thanks for the info anyway I will try and find LaMotte kits. About the fish though I was checking back in my records and it appears I have not checked PH since the beginning of December in the 90 but looking at the records for the 75 it seems the PH has changed from 7.4 to 7.8 since the end of December. Could this have caused the problems for my fish ? < No, this pH range is well within the normal range for Lake Malawi Cichlids.> All the other fish in both tanks seem fine although the barbs seem to be scratching in the 75. I thought that a gradual change in PH is ok but a sudden change would harm all the fish ? < Gradual is ok but sudden shifts in pH especially below pH 7 usually mean that the buffering capacity of the tank is gone and it may be ready to crash.> I have tried to include a couple of photos to see if you can see the difference in colour between the two fish . Image 471 shows the sick fish and 473 shows a healthy fish. < Sorry, the photos did not make it.> Any ideas ? < If the tank is in good shape with no excessive nitrogen problems then I would start looking at possible protozoa infections. It is similar to ich but does not develop any white spots. Try treating the tank by heating up the water to 82 degrees and see if that makes any difference. Then I would think about treating the tank with clout.-Chuck.>

Hardness in whatever units I was using a test kit that had the dKH norm as 8-12. I have since switched to a La Motte alkalinity test kit that gives the reading in ppm. I am not having any luck in finding the normal range for alkalinity in ppm. Can you please help? (a previous email to you guys about 2 weeks ago on the same subject was answered as we do not have a clue and good luck. That really is not the answer you guys meant to give, was it?) <Mmm, here's a link to Ozreef's conversion twixt ppm, milliequivalents per liter... for dKH: http://ozreef.org/reference/alkalinity_conversion.html Bob Fenner>

Hardness values Thank you Mr. Fenner. Your book is great and I  read it all the time. This chart shows a normal range of 151.8- 303.6 ppm or dKH of 8.5- 17.0 as the normal range. Do you agree with that range. Thanks again! <Yes to the "normality" of this range. There are certainly municipal waters that are harder (and are best dealt with by diluting with R.O. and/or Deionized water) and a scarce few that are softer that can be added to with commercial preparations. Bob Fenner>

Too low pH, Too High GH & KH Hi Crew, I read some of your FAQ via search and found some useful information. I a problem I've not seen. I have a 55 gal fresh water tank. almost a year) My problem has been having well water that has a pH of ~5 and a KH of ~30. I've done frequent water changes to lower the KH. This also lowers my pH also. Can I do any of the following? 1.Use KOH to increase the pH. (Will this add too much Potassium to the tank?) 2.Treat RO/DI water to raise the PH before making water changes? 3. Of course your suggestions. My fish which range from various tetra's, angles, guppies and loaches seem to be happy but I am not comfortable with a pH of 5.5. The GH reads about 75-100 < Well water is always a little tricky. Take your pH readings directly out of the tap and then place some water in a 5 gallon bucket and let it sit overnight. The next day read the pH and compare that to the reading right out of the tap. If the pH right out of the tap is lower then there is probably some CO2 (Carbonic acid) in the well water. You should then let you water sit for 24 hour before making any changes to the water chemistry. I would recommend using a buffer to bring the pH up to a more stable 6.5. Check out some products by Kent or SeaChem to buffer the water. Add some to a bucket to get it where you want it and make sure it is stable before slowly adding it to the aquarium. All changes to the aquarium water chemistry should be gradual to avoid stressing the fish.-Chuck> Johnny

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