Extremely low pH in blackwater tank.

seangee

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Please note this is in the scientific section and my general recommendation of 50-75% weekly water changes still applies.

Now that's out of the way I am setting up a new blackwater tank and aiming for very soft acidic environment and would be happy if the pH could get to around 4 but will not add anything to the water to achieve this.

In my community tank I use RO, have bogwood, have a good number of plants and am heavily stocked. Ideal conditions for a low pH. But the tank never drops below 5 - according to a digital tester its typically around 5.3. In this tank I do regular 75% weekly changes and we know that this contributes to a stable environment.

Much of the guidance on very softwater fish suggests water changes of no more than 25-30%. I do believe that large changes are still beneficial as long as performed regularly with stability being the key.

But...
  1. Is there a case for keeping a light stock level and reducing the weekly water changes to 30% to allow the pH to drop further?
  2. Is the assumption that pH would continue to drop naturally (with these smaller changes) due to natural biological processes correct? The source water has 0KH so there is no buffering
  3. If the above 2 items are correct is there any detriment to doing a larger monthly change of say 75%. Besides my natural obsession with clean water my thinking is that this will prevent the pH dropping out of control and keep it at a level where it would still be safe to perform an emergency water change (if needed) without shocking the fish.
 

Colin_T

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Why do you want a pH of 4?

If you have 0 KH and the pH isn't dropping below 5.3, then it probably won't drop any further regardless of water chances, unless you add heaps of food to create more nitric acid and force the pH lower.

Very few fish naturally occur in water with a pH of 4 so you are risking their lives by trying to drop it that low. If you have the pH at 4 and you water supply changes and is suddenly above 7.0, you can cause alkalosis in the fish. This is caused by a sudden rise in pH and can kill fish. If the pH is 5.3, it's less likely to happen but still can.
 
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seangee

seangee

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Very few fish naturally occur in water with a pH of 4 so you are risking their lives by trying to drop it that low. If you have the pH at 4 and you water supply changes and is suddenly above 7.0, you can cause alkalosis in the fish. This is caused by a sudden rise in pH and can kill fish. If the pH is 5.3, it's less likely to happen but still can.
Not that uncommon in the Amazon basin and if you want to keep / breed wild caught fish...

My water supply is RO :)
 

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