Extremely low pH in blackwater tank.

[seangee]

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]

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.

 

[seangee]

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

 

[Anthony1976]

I think I read somewhere if the ph drops below five your cycle can stall ? And as already said if ph goes from very low to above 7 ammonium changes to ammonia which is a real killer.

 

[seangee]

I think I read somewhere if the ph drops below five your cycle can stall ? And as already said if ph goes from very low to above 7 ammonium changes to ammonia which is a real killer.

Heh heh. Tank has stabilised at around 5.5 even with my 75% water changes. No chance of bacteria surviving in there. Plenty of plants so I avoided all that mucking around trying to establish a cycle and all is good in the tank

 

[WhistlingBadger]

Mmmm, sparkling gouramis. High on my list for my next nano tank. Please tell me about them so I can live vicariously through your experiences.

Many of the rarer blackwater species of southeast Asia, particularly Malaysia/Indonesia, need a pH of 3-5 to truly thrive, conditions that would kill most other fish. I would guess that 5.5 would be sufficient even for these species.

My experience, via Walstad (peace be upon her), is that in a densely planted tank you can back off quite a bit on the water changes. I'd say that smaller changes, maybe 10%/week, will keep your pH more stable and still keep the water clean enough.

 

[seangee]

Mmmm, sparkling gouramis. High on my list for my next nano tank. Please tell me about them so I can live vicariously through your experiences.

Many of the rarer blackwater species of southeast Asia, particularly Malaysia/Indonesia, need a pH of 3-5 to truly thrive, conditions that would kill most other fish. I would guess that 5.5 would be sufficient even for these species.

My experience, via Walstad (peace be upon her), is that in a densely planted tank you can back off quite a bit on the water changes. I'd say that smaller changes, maybe 10%/week, will keep your pH more stable and still keep the water clean enough.

Not going to stress about it. According to SF everything in there is in range except the pygmy cories which are quoted as being 6.4 - 7.4. With 0KH I will stick to the large water changes to avoid shocking the fish if the pH drops too low and I ever need to do an emergency change. Tank is also <coff> reasonably well stocked and the sponge filters at low flow are not nearly as effective at mechanical filtration as a "proper filter". The chillies have the lowest quoted range (4-7).

Love the sparklers. There is some aggro (note the tattered tail) but I have 6 in there and they tend to keep it between themselves. They occasionally chase the chillies - but never catch them and don't try too hard (they can be relentless when chasing each other with some of the disputes lasting hours or even days). All hostilities are suspended at feeding time and they will happily share a pellet with anyone in the vicinity. I'm keeping a close eye as I'm not sure what will happen when they start breeding. They have had a few false starts (practice bubble nests) but I suspect they are still a little immature.

 

[kwi]

I'm just commenting so I got notifications, my tap water is soft and slightly acidic and I have become quite interested in doing a black water tank, even considering my local river water which is peat filtered.

 

[Retired Viking]

Tanks look good, How is stumpy doing? I am down to 4 embers but hope to puy some more soon. My RO tank is down to around 45ppm but the PH is 7.5-7.8.

 

[seangee]

Tanks look good, How is stumpy doing? I am down to 4 embers but hope to puy some more soon. My RO tank is down to around 45ppm but the PH is 7.5-7.8.

She's cool. I was watching her today and the shape and length of her fins is identical to the others. She still has the white scar line on her tail and her dorsal fin has stayed completely clear - so I can identify her. Otherwise she looks like a perfectly healthy little ember.

 

[Retired Viking]

She's cool. I was watching her today and the shape and length of her fins is identical to the others. She still has the white scar line on her tail and her dorsal fin has stayed completely clear - so I can identify her. Otherwise she looks like a perfectly healthy little ember.

That is good to hear

 

[HoldenOn]

Not going to stress about it. According to SF everything in there is in range except the pygmy cories which are quoted as being 6.4 - 7.4. With 0KH I will stick to the large water changes to avoid shocking the fish if the pH drops too low and I ever need to do an emergency change. Tank is also <coff> reasonably well stocked and the sponge filters at low flow are not nearly as effective at mechanical filtration as a "proper filter". The chillies have the lowest quoted range (4-7).

Love the sparklers. There is some aggro (note the tattered tail) but I have 6 in there and they tend to keep it between themselves. They occasionally chase the chillies - but never catch them and don't try too hard (they can be relentless when chasing each other with some of the disputes lasting hours or even days). All hostilities are suspended at feeding time and they will happily share a pellet with anyone in the vicinity. I'm keeping a close eye as I'm not sure what will happen when they start breeding. They have had a few false starts (practice bubble nests) but I suspect they are still a little immature.

You make me want sparkling gourami .

 

[itiwhetu]

Heh heh. Tank has stabilised at around 5.5 even with my 75% water changes. No chance of bacteria surviving in there. Plenty of plants so I avoided all that mucking around trying to establish a cycle and all is good in the tank

You know it's really acid when, you put your hand in the tank with a cut on it and it tingles!!