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ed seeley 01-22-2007 12:33 PM

Experience with pH crashes; Do they really happen?
Hi everyone,
This question stems from a discussion in a Killifish mailing group where one of the members had suffered a fish kill that he said was due to a pH crash.
He had measured the parameters in his tank after the die-off. His pH had dropped to 4.5 from the usual 6.5. He was using RO water with a pH 6.5 buffer.

He got lots of advice from the other members about buffering his KH, not just using a pH buffer, nut adding more KH to the water. Products to raise the KH were said to be 'essential'.

Personally I use RO water with Kent RO right, and relayed my experience of using that and maintaining my tanks with a KH of zero. This is with no added CO2, Fermented CO2 and Pressurised CO2 on various tanks.

My questions are these;
  1. Do pH crashes occur and what tank conditions are typical when they do?
  1. What causes pH crashes?
  1. Is it the pH crash that causes fatalities or are pH crashes merely a product of other problems in the tank that have caused fatalities?

In other words, do pollutants build up, poison the fish, but then get broken down by the filter producing acid that drops the pH and then you turn up the next day to a tank with a lowered pH and dead fish and, measuring the parameters, find the pH as the obvious change and blame a 'crash'?

I'm not convinced that a pH drop, in itself, would be so disastrous. I think something must cause the pH to drop and what is this? Why does it seem to have such drastic effects? Is it the often trotted out 'running out of buffers'? If so why does my water, with no measureable buffers, not crash constantly and all my fish die?

Please add all your experiences and thoughts.
I am looking for any first hand evidence of, and dealings with, pH crashes, not the heresay and myth that is spread around.

What about those of you, who, like me, use water with almost no buffer? Have any of you had a crash?

Bert H 01-23-2007 03:53 AM

I have no personal experience with this. But here's a post which you might find interesting: It's an interesting read.

Squawkbert 01-23-2007 05:02 AM

The way I've heard it for aquariums, a pH crash is either
a) excess CO2 into an unbuffered tank causes pH to drop fast
b) CO2 stops, pH rises quickly - again, as a result of having little or no buffering capacity

Having some buffering capacity will help prevent situation (b) from happening, but having the pH change fast enough to kill fish isn't likely anyway as the pH will rise gradually as the CO2 diffuses out of the water.

Situation a can only happen with a pressurized system and only when it fails in the on position, injecting lots of CO2 too quickly. Even in that situation, I din't know if saturating aquarium water w/ CO2 could bring the pH down to <5. Buffering capacity would help a little, but w/ unlimited CO2, the pH will still drop. If it drops quickly, fish will die (probably from lack of O2).

ed seeley 01-23-2007 01:02 PM

Thanks Bert, just about to have a read of that.

That's kinda my point though Squawkbert. I've heard about it (and heard the tales about it), but never experienced it. And all my tanks, including a 20L one have 0dKH. Some are way over-stocked (according to the guidelines!), but I've got Nitrate below 12.5 and every other parameter 0 or where it should be! Three have CO2, one pressurized, one DIY and one tablets. None of these seem to have wild pH fluctuations though and the fish are healthy and breeding.
The killi keeper who was the source of this had a small tank 12"x8"x8" with low load (6 small killifish) and a few plants. No CO2 and a crash.

You're dead right about a CO2 dump killing stuff, but I think that's to do with Co2 excess and O2 shortage killing the fish not a pH crash. That shouldn't have happened to the killi tank.

Thanks for the post though, I do appreciate everyone's contribution. It's good to hear your views.

Does anyone out there use very soft water like me without problems???

Salt 01-24-2007 04:42 PM

According to some of the recent posts I read, no, there is no such thing as a pH crash... it is a myth.

What happens is a person goes to their tank and finds dead fish. They test their pH and find it's super low. So they say they had a pH crash because their KH was too low. But all that's happened is a CO2 overdose. That's what killed the fish. Had their been a higher KH, the pH wouldn't have been super low, but the fish still would have died.

That's the theory anyways.

dennis 01-24-2007 04:55 PM

AFAIK, the idea of a pH crash was around long before we started adding CO2 to the water. In that case, I belive what happened was either the plants consumed all the carbonates, thus removing the buffer and allowing naturally produced acids from decomp and fish waste to lower the pH to dangerous levels, or... lack of water changes caused organic acids and natural biological process to slowly remove carbonates, thus removing the buffer and allowing pH to get very low.

I have had this happen on a small 2.5 gallon shrimp tank. I neglected it for a long time and then the shrimp died. It was planted with a bunch of anacharis, which eventually consumed the carbonates and pH was like 5 when I checked it.

Now, as for our typical situation, to the best of my knowledge your only issue with low/no buffer is when using a pH controller to inject CO2, as was already described.

Long story short, could happen with a pH controller and CO2, or could happen with really, really, really bad tank maintenance.

ed seeley 01-25-2007 09:43 AM

Thanks guys,

I'd agree with that totally, but the tank that orginated this new thread was not a planted tank, as we would see it! It had a few killis and, I think a bit of Java moss!

I think his fish were killed by a brief ammonia spike, or some other pollutant, and then this subsided before testing the water. But, as it was treated by the filter, this produced acid that also caused the pH to drop.

What do you reckon? Possible? Probable? ??? :confused:

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