Acidic tank

[mbsqw1d]

I thought I'd ask the question about keeping an acidic tank. I've noticed a few posts recently where new aquarists have naturally low KH source water and are asking good questions about cycling. Our instinct is to advise raising their water's KH to ensure the pH doesn't drop low enough to the point where nitrification ceases.

They appear to be in a tricky spot where really, they're potentially in an ideal and envious situation - depending on what fish they wish to keep.

The tricky part is that their source water may have a starting pH of around 7, however their KH is low, and so days into cycling, the nitric acid created from nitrifying bacteria eats away at the miniscule KH and creates an acidic environment, thus stalling the cycle - ammonia in low ph conditions exists as ammonium.

Ammonium is harmless (?) to fish, and so if someone keeps (suitable) fish in a low ph tank where ammonium exists, they do not need to concern themselves with a cycle. Many people who keep such fish might use RO water to ensure such conditions exist.

Old Tank Syndrome (OTS) is where a neglected tank's water has become acidic due to the build up of (not just) nitric acid which has "eaten away" at the buffering KH. The ammonia exists as ammonium and the fish are living relatively ok. The owner decides to perform a water change and in doing so, raises the ph back up to their source water's value. The ph goes up and the ammonium switches back to deadly ammonia, killing most of the fish.

If a person has low kh source water, yet the ph is around 7 and they want to keep acidic fish (betta, corydora, tetra, gourami....), they'd be best keeping an acidic tank where the normal nitrogen cycle doesn't apply. What is the best advice for them?
Because come water change, they're going to raise the pH and experience OTS.

@Essjay (cycling specialist)
@itiwhetu (acidic tank connoisseur)
@Byron (God)

 

[StevenF]

My tank wants to go acydic due to the GH booster I use. yet I can keep it at 7 with no difficulty. I place a decorative sea she'll in the tank. When the water goes acidic due to excesss sulfates, chlorides, and even nitrite, the acids will react with the shell converting the acid to PH neutral GH.I have to replace the shell about once a years.

Seashells are made of calcium carbonate. The shell will do nothing if the PH is above 7 and therefore has no affect on PH. But when the tank goes acidic it reacts and pushes the pH back up to 7.

I strongly advise against using KH boosting products. They contain sodium bicarbonate or Potassium bicarbonate. If used these can create an imbalance of between sodium and potassium. If the water is mostly potassium or sodium this can make the water toxic to fish. In most streams and rivers most of the kh comes from dissolved calcium carbonate or magnesium carbonate.

 

[itiwhetu]

I completely ignore source water information. I know that the water from a town supply will be Alkaline, that doesn't bother me. All I care about is the parameters in the tank. If you use natural neutral gravel, plant the tank to around 50% of its volume and perform around 25% water changes weekly your tank will remain fairly stable. You can adjust the exact amount of water you change by putting a mark on the tank, which indicates how much water you take out. The figure doesn't really matter. You aim for a constant pH of around 6.8. Sure if you get down to the low 6's you are going to have problems but that won't happen in a week, changing water from a town supply.
There will be members using Well water, RO water, Rainwater and dozens of mixes at the end of the day 25% water changes will maintain any tank at a constant level. The huge water change brigade are the ones that have trouble with fluctuations, not those that do a little often.

 

[Naughts]

I completely ignore source water information. I know that the water from a town supply will be Alkaline, that doesn't bother me. All I care about is the parameters in the tank. If you use natural neutral gravel, plant the tank to around 50% of its volume and perform around 25% water changes weekly your tank will remain fairly stable. You can adjust the exact amount of water you change by putting a mark on the tank, which indicates how much water you take out. The figure doesn't really matter. You aim for a constant pH of around 6.8. Sure if you get down to the low 6's you are going to have problems but that won't happen in a week, changing water from a town supply.
There will be members using Well water, RO water, Rainwater and dozens of mixes at the end of the day 25% water changes will maintain any tank at a constant level. The huge water change brigade are the ones that have trouble with fluctuations, not those that do a little often.

Are you saying that by changing 25% of the water each week the pH will lower, even if the source water is basic (say 7.5 for example)? How long would that take to change it to 6.8?

 

[GaryE]

A few years ago, I had to adjust to tapwater that liked to slide acid, I loved it, but its instability at times meant I had to be more rigid with 25-30% water changes than I had before. I kept rainforest fish, and all was well, as long as I took care of the tanks.

It's left me a little dismissive of the cycling process.

Unlike @itiwhetu , I consider source water among the most important things an aquarist can look at. It may be because I have moved with my tanks more often than many. People who live in one place for a long time sometimes forget how variable conditions can be for others. There are aquarists far from cities in agricultural areas who get water that's worse than what I change out. Here, with great water, I would love to have a continuous water change system, but that's a project for another time.

Changing 25% weekly with the water I had in my last 3 homes kept the water exactly at the parameters that came from the tap, in hardness and pH. It's the constant level @itiwhetu mentioned. Would it be the same with whatever water you get from the tap? Maybe. Probably.

Having managed tanks where the pH was in the low sixes, all you do is change 25-30% of the water every week, stock lightly as you should anyway, and choose fish that evolution has adapted for low mineral acidic waters. If you decide you want hardwater fish, it's easy to harden water (hard to soften it - adding is always easier than removing) but you'll probably need a test kit.

The old tank effect is there, no matter what the hardness. You have to keep water turning over. In the dry season of many tropical regions, rivers break up into chains of evaporating ponds and fish are caught in them. They go into a sort of waiting state, conserving energy waiting for fresh water from the rains. They can last a while like that, and that phenomenon seems to be the basis of the balanced no water change aquarium school that still rears its head on forums, even though the hobby moved on from it sometime in the 1980s.

My advice to aquarists in the situation you asked about. Read about fish. Choose wisely. Change water regularly. Enjoy.

If you get a kick out of reading reagent test kits, you won't have fun - there won't be much to read. You'll have to read the fish instead.

 

[Naughts]

Changing 25% weekly with the water I had in my last 3 homes kept the water exactly at the parameters that came from the tap, in hardness and pH. It's the constant level @itiwhetu mentioned.

So you're experience is the pH stays the same, for example 7.5 will not drop to 6.8 so you can't "run an acidic tank" with basic water?

 

[GaryE]

So you're experience is the pH stays the same, for example 7.5 will not drop to 6.8 so you can't "run an acidic tank" with basic water?

You're into holy grail territory for people who keep rainforest species. I wish it were easy to magically drop hardness.
Well buffrered water is very stable. Years ago, I put my 140ppm, pH 7.4 tap into an unused tank and poured phosphoric acid in, til I had a pH of around 5. A couple of hours later, pH 7.4 again. In my current water, where I have moved to, that experiment would have different results. Remove the mineral buffers via reverse osmosis, and you can have a tank with nice acid water. Or live in a place like where I am, where there is a pleasant tannin tinge to the tap water, drawn from blackwater lakes.

But always remember 'basic water' is different to everyone. It confuses our conversations, because while pH 7.0 is the real baseline, very few aquarists stop and think that the person they're talking to can live in a different environment, even nearby. Tapwater in central Montreal is medium hard, but in the west of the same small island, quite soft. We don't share the same reference points.

 

[Naughts]

You're into holy grail territory for people who keep rainforest species. I wish it were easy to magically drop hardness.
Well buffrered water is very stable. Years ago, I put my 140ppm, pH 7.4 tap into an unused tank and poured phosphoric acid in, til I had a pH of around 5. A couple of hours later, pH 7.4 again. In my current water, where I have moved to, that experiment would have different results. Remove the mineral buffers via reverse osmosis, and you can have a tank with nice acid water. Or live in a place like where I am, where there is a pleasant tannin tinge to the tap water, drawn from blackwater lakes.

But always remember 'basic water' is different to everyone. It confuses our conversations, because while pH 7.0 is the real baseline, very few aquarists stop and think that the person they're talking to can live in a different environment, even nearby. Tapwater in central Montreal is medium hard, but in the west of the same small island, quite soft. We don't share the same reference points.

OK, so (unless you RO) you're stuck with your source water and the interaction of it's GH, KH and pH which is back to what I have previously understood.

Hopefully @itiwhetu can shed some light on it. If there was a way to make the tank acidic just through a particular maintenance strategy I would try it.

@mbsqw1d, I know @Byron and @seangee have said that in their heavily planted tanks the low GH/KH/pH doesn't cause any problems as long as it is stable, even as low as pH 4 or 5. I assume the plants are processing the nitrogen so cycling beneficial bacteria become irrelevant.

 

[itiwhetu]

Tanks will naturally go acidic if there is enough organic matter in them. As organic matter decomposes, then it produces acids, those acids will lower your pH.
I never vacuum my tanks, I have driftwood in them and a huge amount of plant all of these things contribute to the organic matter load on the tank.
Plants will also remove a certain amount of the minerals from your tank, and as you remove plants because your tank is overgrown you remove that mineral content as well.
All aquarists try to have their tanks too clean; fish don't need really clean conditions to survive and do well, and organic waste decomposition is a vital part of having a stable aquarium

 

[GaryE]

Tanks will naturally go acidic if there is enough organic matter in them. As organic matter decomposes, then it produces acids, those acids will lower your pH.
I never vacuum my tanks, I have driftwood in them and a huge amount of plant all of these things contribute to the organic matter load on the tank.
Plants will also remove a certain amount of the minerals from your tank, and as you remove plants because your tank is overgrown you remove that mineral content as well.
All aquarists try to have their tanks too clean; fish don't need really clean conditions to survive and do well, and organic waste decomposition is a vital part of having a stable aquarium

Again, it depends on the source water. I don't gravel vacuum often, sometimes years,. and there is organic matter in all my tanks. In my well buffered water "days", the tanks didn't budge from pH 7.4. I tried everythings - I wanted more acid water before I understood pH didn't matter much, and it was water hardness that affected hatching, breeding, etc.
In my house before this, and I suspect here since the water is similar, pH would drop in time. I find allowing organic debris provides a great habitat for Oodinium parasites though, so I handle things cautiously. Water changes are never skipped.

20 years ago, I was trying to breed a Cichlid, Dicrossus maculatus, and a friend in the US was reporting success as the pH plummeted in his kind of neglected tank. I tried the same thing to no avail, with my old buffered conditions. Source water matters.
I never did breed those beauties. Never did get to his pH 5.5 water.

 

[Byron]

As a couple members have mentioned, it is not wise to ignore the GH, KH and pH of the source water. This is what governs the whole process. People who attempt to adjust the pH on its own fall into this trap; it is the GH and KH that influence and indeed determine the pH. The higher the GH and/or KH, the more "buffering" capacity there is, preventing acidification.

In my situation, until recently, I had source water with a basically zero GH and KH, and the pH was in the 5 range. I keep soft water fish, so this was ideal. Depending upon tyhe organics in each tank, the pH would settle at 4, or 5, or6 something, and stay there, for years, with weekly partial water changes of 50-70%. This worked because the source water remained the same with no inherent buffering capacity, and I did nothing to increase GH/KH/ph except through the use of plant additives, which were obviously necessary under such a low GH, but these were not anywhere near sufficient to mess with the GH/KH/pH.

 

[itiwhetu]

If your tank is not going acidic it will be because of the substrate. A lot of the time not enough attention is paid to the buffering capacity of the substrate

 

[Byron]

If your tank is not going acidic it will be because of the substrate. A lot of the time not enough attention is paid to the buffering capacity of the substrate

This is a candidate, if the substrate is calcareous. But the GH/KH are still the prime motivators. The stronger they are, the less acidification can occur. The example in post # 7 above where adding acid lowered the pH but within hours it bounced back up. The GH/KH controls water chemistry respecting pH.

 

[Kolykaf]

I really only keep soft water fish and use R/O water for all my water changes. I bring the Gh to 4-5 degrees and all of my tanks have a Kh of 1 or below. The ph of the R/O is around 6.5, and it’s pretty much the same in my tanks. The exception is my 75 gallon where I run CO2. It drops a little bit when the gas is running, but not by much. I do regular water changes (25-50% weekly to every other week) on all tanks. My substrates range from plain sand to gravel to organic potting soil with a cap. I also have driftwood and botanicals in all of them. My tanks have been running with almost no Kh for years with no problems.