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>