Water and PH

Hi guys

I'm hoping @Dirk will also get involved here and shed some light.

My question circles around water and its ph and stems frommy current attempts to get Wild Tefe Green Discus to spawn.

I dont want this to turn into a discussion on correct or incorrect ph and ph stability etc, my aim with this discussion is not to discuss that.

Let me start by explaining the question.
In the tank which holds my Green discus I run a water mixture of approximately 90% RO water and 10 % Tap water. Nothing gets added to this water to prevent the ph from dropping, and apart from a small sachet of crushed coral in the filter, the ph is allowed to go very low.
I am limited in my ability to test the water, my tester can only test as low as ph4.5, but can honestly say that the tester indicates an even lower ph, as 4.5 is achieved immediately. So I estimate the ph at between 4 and 4.5.
Now being RO water mostly, with no buffering capacity at all the ph in the tank will theoretically continue falling, especially considering that the tank contains lots of driftwood, and the filter a great deal of Spaghum Peat moss.

My question is - if I should delay water changes and just leave the tank to run as is - to what level will the ph drop before it stabilises, and what would the chemical reason be for it to stabilise.
In different words - surely the ph will not drop to ph 2.5? And if it stops as say 3.5, what prevents it from dropping more?

Hope I get a nice discussion going here

Rgds

Marco

 

Hi Marco Two quick questions: What pH tester are you using?What pH are you aiming to achieve?I understand the discussion is not centred around what the ideal pH should be. Andrew

 

Hi @pHish_man

Andrew, Ive got two ph testers. One is a pen type and the other Nutrifin drops. I use them together so as to be able to gauge accuracy. Unfortunately the drops only test as low as 4.8, and the pen is only rated to test to 4.5.
I recently took the water for more accurate testing but due to its softness the LFS couldnt test it, but kept getting error messages

I am not really aiming for a specific ph to be honest. Im not trying to get it any higher in fear that doing so could then result in a sudden drop again, and my water maintenance is of such that before the fish look uncomfortable, which apparently will happen below 4 the water is changed stabilising it at +-4.5 until the next w/c.

Rgds

Marco

 

Interesting question. It's interesting that your crushed coral... which a lot of people are using to maintain a higher kH (which in turn, effect pH swing) is still allowing the pH to drop as low as what you are reading.

I'm convinced that your pH will eventually stabilize at a certain level, (which would be interesting to determine) because even though you are only adding 10% tap water, you are still adding a source of Carbonate Hardness. The crushed Coral will also be a contributing factor here.

 

Hi Marco

The pH will stabilize eventually. As you probably know pH is the -log[H+] concentration. The higher the conentration of H+ the lower your pH will be. But eventually you will reach a pH in which will not allow significantly more H+ to be added by the dissolution of the coral and the peat moss. And since it is a log value a lot of H+ ions will be needed to change the pH value.

 

@TheGrissom

Thats exactly what I have thought. Meaning to say that it cant possibly keep falling as low as say 2, without adding a serious amount of some acid compound. That would mean if left long enough the water will turn into acid.
So then, if Im understanding this correctly, it means that the ph would stabilize, but it will do so not because of a natural buffering in the water. It will stabilize because too many H+ ions would be required to lower it further, and the natural process will simply not "create" enough of these ions? So the only way to then further lower it (not that I intend to) would be by adding these ions from an external source such as muriatic acid

At what level, theoretically would you guess it to stop. I have a "pen pal" in the USA who tried to breed Heckel Discus and he indicated that his water, which was 100% RO dropped as low as 3.7 but then never went down any further. Is it possible that 3.7 would thus be the basement water can reach without further adding acidic compounds?

Rgds

Marco

 

Am I right in saying that it is an ion exchange? Similar to that of an oxidation/reduction reaction? Eventually it will reach a point where the water will be the same pH as the coral.

 

@Marco

By having a pH of lower than 7 the water is already an acid technically. An acid can be defined as anything that can donate a proton and since these are in excess in acidic medium it will suit the definition. Once it has stabilized then an external source of protons will be needed to further lower it. The pH stabilizes because an equilibrium is reached. Many substances will dissolve in solution and thereby alter the pH but once the pH reaches a certain point the substance will no longer be soluble. In the case of the coral carbonates are being released into the water. These combine with the water to form HCO3- which is a weak acid but as the pH drops the coral becomes less soluble. That is why the pH stabilizes. Any other H+ that does end up in the water is not at a high enough concentratio to make a difference to the pH. If the pH does happen to rise slightly the coral dissolves again. Its called le chatilliers principle.

 

@Firefly: Its not ion exchange. The coral gives up its ions and gets nothing in return. Also the coral does not have a pH. Solids cant have a pH because solids do not have any free H+ ions. I think I answered your question in Marcos answer

 

@TheGrissom

Great answer! Thank you very much for that.

If you dont mind - have you got any idea at which ph level the water will actually stabilize?

Rgds

Marco

 

Hi Marco,

You asked me to get involved so here goes. This issue is complicated and requires quite a considerable amount of background chemistry. I would like to explain each of the factors that contribute and then make a combined conclusion:

1. Your handheld pH meter does not have the ability to measure pH accurately in the lower range and so do the drop tests not have the ability to measure pH at these lower levels and you have confirmed this. I just want to add that drop tests are very dependent on water hardness and if it is low are very inaccurate and cannot be relied on at all, so as you have said you cannot rely on the drop tests. The electrode of any handheld pH meter is totally inadequate for measuring pH in soft water. The electrode just simply does not cope. The electrode requires other salts in the water in order to conduct electricity to be able to perform the measurement of the pH and if it is too low then the electrode just drifts, it cannot measure anything. For the measurement of pH in very soft water, you need a pH meter with a separate laboratory style electrode, this is the only pH measuring device that can work. However, I know that you are fully aware of this and my comment is not meant as a criticism but rather to explain why your measurements do not work. In my opinion, if you want to keep discus in the long run and want to do these measurements accurately, you need an accurate laboratory style pH meter and you will have to invest in such a device, but there are good models that can be purchased at reasonable prices, so this can be done without breaking the bank completely.

2. If you mix RO water with tapwater, you are reducing total hardness and carbonate hardness considerably, and if you reduce carbonate hardness the water has very little buffering capacity against pH drops. Carbonate hardness is carbonate and bicarbonate which are dissolved in the water and as soon as protons, H+, are released in the water, the carbonate or bicarbonate reacts with it and it will therefore not contribute to the concentration of the H+ ions and therefore not contribute to the drop in pH.

3. After having done a number of water changes in the way that you have explained, then the logs are no longer contributing to the drop in pH, about that I am absolutely sure, the ability to release tannins and to reduce pH drops very rapidly. So in my opinion, the drop in pH is NOT being caused by the logs any longer.

4. The next factor we have to consider is the crushed coral you have added. Crushed coral consists of calcium carbonate but it is not dissolved, it is sitting there and acid can and will attack it and react with it in the typical reaction that protons react with biocarbonate (which forms a part of carbonate hardness). What this means is that it can buffer the pH, as many of you have commented on. However, there is a condition here which is critical. The ability to react with crushed coral is dependent on the surface area of the crushed coral and if the amount that you have in the tank is small, say something like two tablespoons it is not enough and the pH can and will drop. A further factor regarding crushed coral is that it becomes coated with organic molecules very rapidly, the technical term that is used is that it is fouled, and then it does not do any buffering any more because the surface is not exposed to the water any longer. What you need to do is you need to take the crushed coral out of tank ever so often and give it a good scrub to remove the organic layer that forms over its surface. I would also like to mention that you can replace crushed coral with shells which also consist of Calcium Carbonate and I use this in all of my tanks to stabilize the pH because of the very soft water that we have here in the Cape.

5. The final point that I wish to make is however the most important and one which all of you have missed. When you keep fishes you feed them proteins because proteins are the building blocks and fish grow because they are incorporated in the diet. What is not however commonly understood is that fishes break down a major proportion of the proteins in the diet to obtain energy instead of using them as building blocks. When proteins are broken down for energy purposes, the amino group of the amino acids is split off the amino acid and released as ammonia. All of you actually know this because we talk about "biological filtration" all the time in fishkeeping and this involves the breakdown of Ammonia, NH3, to nitrite, NO2-, and finally to nitrate, NO3-. Without writing any complex reactions, you can see that the N releases the H and reacts with O, oxygen, to form nitrate. The H goes into the water in the form of H+, or protons, or acid, and this causes the pH to drop.

So the combined conclusion:

Marco you are feeding your fishes well with a high protein diet as a result of which they are forming loads of ammonia which is being converted to nitrate in your filter and which in the process is releasing loads of H+ ions which is causing your pH to drop drastically. Your crushed coral is coated with organics and is not able to buffer any longer or it is just simply too little to do the buffering. My advice is that you should wash your crushed coral to remove the fouling, you must really rub this in your hands to scrub it clean. Then you must use more of the crushed coral because what you have added is not enough the stop the pH drop. You need an accurate pH meter to measure the pH accurately. You must not think that because you cannot measure the pH so low that it cannot drop more. It will drop more and more and eventually become as corrosive as battery acid and you cannot just think that this is going to stabilize, it will not unless you do something or else your fishes will die, it is as simple as that.

Kind regards,

Dirk

 

Hi @Dirk

Thank you for the long and detailed reply.

I agree with you that its the bio load dropping the ph so low. Of course having giant heaps of peat moss and a continuous supply of Indian almond leaves in the tank is not helping the ph at all either.

At the moment though Im not too worried about it dropping any further as my water maintenance is of such that I continuously replenish water and add clean water with regular water changes.
Im aware of the risks but of course I manage this as best I can.

I was more, which you have now answered, interested in the waters ability to keep dropping. I was actually convinced by mere reasoning that at some stage it would become virtually impossible for the ph of the water to fall any lower. Thats now irrespective of the fish being alive or dead - not that I intend allowing it to happen. I figured that at some stage natural "buffering" of some sort would prevent it (as @TheGrissom explained) from falling to say a ph value of 2

I was really more interested in the chemical intricacies required to push it that low.

On a side note - its incredible to see these fish in water such as this. You saw them when you visited recently - and as far as the Wild Greens are concerned, its almost as if the lower the ph value the prettier they get. The male Green at a ph of 6.5 looks totally different than what he does at a much lower ph. In this extremely soft acidic water he resembles a Brilliant turquoise in some ways, with his body completely bathed in a soft metallic like turquoise sheen, with the added red spots. At a higher ph the red spots become less pronounced, and the nice turq sheen fades to only striations.
Most fish would certainly baulk at these water parameters but these are happier than ever, eating from my hand and in constant "show-off" mode. Nature never ceases to amaze

Rgds

Marco

 

Hi Marco,

I would like to warn you against being careful with further pH drop. Jason recently had a pH crash with the pair of discus from which he got the younsters, which resulted in the death of his red turquoise female. I have also had considerable problems with discus if the pH goes below 3, so please be careful, I would not like you to loose that beautiful pair of discus.

You are quite right that if you reduce the hardness as you have and you add plant tannins to the tank how healthy and colourful your fishes can actually get. This actually illustrates how much better discus do if the water conditions are right, but you have to be very careful with soft water because it is so plastic, and by that I mean the pH is not stabilized and can drop as you explain. I am strongly opposed to persons adding acid to the water in a discus setup because this can drop the pH far too quickly, and secondly, it does not really help in harder water, you need soft water to keep discus, not only low pH water.

Kind regards,

Dirk

 

Hi Marco

I have no idea at what pH the water will stabilize. Maybe establish this experimentally. Just not in your tank.

 

Just my 2c, but since the fish waste is at least partially responsible for the PH drop, it would be impossible to do this outside the tank. For the average person, experimentally creating the same conditions as in the tank would be near impossible...

 

@KillerBunny: fish waste will actually neurtalize some of the H+ (NH3 excreted becomes NH4+) but besides this the fish waste will be negliable as long as there is more coral to dissolve. But water from the aquarium can always be added to the experiment on a daily basis if that is desired.

 

I was basing my comment on the fact that both NH4 and NH3 will be broken down to NO2 and NO3 during filtration - Leaving extra H+ ions . My point more importantly was that I don't see anybody without some serious lab equipment to measure everything replicating their tank conditions in an experimental setup.

 

Hi guys

Bottom line here is, although purely out of interest sake I would love to know exactly how low the ph would drop, I have no reliable means of checking lower than 4.5, so for me its purely hypothetical.
I was merely hoping someone here would be able to give an idea, chemically at which point further lowering by natural means would become extremely unlikely.
As said before, I am not clued up on all chemistry, so I rely on logic. From that I logically assume the water going as low as ph1.5 for instance would be virtually impossible,unless we add some sort of external source of H+ ions.

Another reason I thought about this is because I naturally assumed, again assumed, that a large scale ph drop from ph6.5 to 4 would be quite quick and very probable considering the water values. However, Im not so sure that a further drop from ph 4 to say 3.5 would be as dramatic and quick, based entirely on the large quantity H+ ions required to do this.

All things noted now - I just want to add that I keep a very close eye on the tank water. I clean the filter weekly, including the coral, all substrate gets syphoned and glass thoroughly cleaned, and I dont take chances with the ph. I do not however at this stage try to raise the ph, as logic reasoning, as said before, tells me that from where it is now it seems the way I maintain it plus the coral in the filter it seems to prevent the ph from slipping down any further.
The tank houses only two pairs of Discus to 450liters, plus a few German rams. Im sure keeping it steady as I have been should allow for safety.
@Dirk - the problem of course will come in once I try to raise the ph slightly, to about 5.5 to try get these Greens to spawn. It will be a challenge then to keep it stable at 5.5 for a long period, or at least slow down the decline in ph value to such an extent that it is safe for the fish.
I have got some more Coral which I can add to the filter/water column though, and finding the correct balance will be the part where things get dicey and very challenging. The problem per say is achieving a low TDS value along with a stable Ph level - Oxymoron?

Of course if the damn Fish will just spawn and get it over with it makes all this so much easier. . . Buggers!

Rgds

Marco

 

Hi Marco,

You asked how chemically at which pointfurther lowering by natural means would become extremely unlikely so let me explain.

You know that the pH scale is a logarithmic scale, a pH of 7 means that the concentration of hydrogen ions or H+ is 10[SUP]-7[/SUP] mols per litre (which is how concentration is indicated in chemistry terms). At a pH of 6 it means the H+ concentration is 10[SUP]-6[/SUP] mol/litre and so we can carry on until we get to pH 3 say at which the H+ concentration is 10[SUP]-3[/SUP] mol/litre. The way you can work this out mathematically is pH = -log [H+] where the square brackets indicate concentration.

So now pH 7 also means 0.0000001 mol/litre H+ ion concentration and at pH 6 means 0.000001 mol/litre H+ concentration. In order to get from pH 7 to pH 6 you need to add the difference between the two concentrations, in other words 0.000001 - 0.0000001 = 0.0000009 mol/litre of H+ ions. You can easily see that this is a small amount of H+ ions, and so this drop in pH can actually occur quite easily when you feed well and the fishes produce lots of ammonia and if you biological filter converts the ammonia to nitrate with the release of H+.

Now consider the situation at pH 4 which means a concentration of 0.0001 mol/litre H+ ions and at say pH 3 this means a concentration of 0.001 mol/litre H+ ions. In order therefore to get from pH 4 to pH 3 , you again need to add the difference between the two concentrations, in other words, 0.001 - 0.0001 = 0.0009 mol/litre of H+ mol/litre of H+ ions. Now you can however see that this is MUCH MUCH more H+ ions that you need to add to get the pH down one more unit. This is 1000 times more than the amount of H+ ions you have to add to get from pH 7 to 6.

This is exactly what applies in your situation. the initial drop in pH from say 7 or 6 to say 4 will happen quite easily because the actual amount of H+ ions that have to be added to drop the pH by this much is relatively small, but as you go further down the amount of H+ that needs to be added is orders of magnitude larger.

So the pH will drop more slowly as the water's pH goes down. The point that we have made though, is that discus do not tolerate pH values of below 3 very well and you therefore need to be very careful if you are getting this close to that pH. However, if you do regular water changes and if you do wash the coral in the aquarium, this is less likely.

Not too difficult to understand, I hope.

Kind regards,

Dirk