Help, Tap Water Ph Crash!

[rossyk]

Hi all. I've had my 60L planted tank up and running for nearly 6 weeks and it was happily cycled. My stock is 6 glowlights, 4 amano shrimp and 4 peppered corys.
 
Well, yesterday I did a routine change (about 25%) and gravel clean, and all seemed well. Suddenly I noticed one of my corys struggling - floating upside down at the surface, only moving if prompted). That was late last night. This morning he was dead. I checked the water. Ammonia was 0.6 - up from pretty much 0 yesterday, 0 nitrite and barely any nitrate. Confused (I'm a newbie to this stuff!), I checked the pH, which has always been around 6.5 in the past. It was at 5! I immediately checked the tap water pH, and low and behold, it was 5 - where it' always been around 6.5 before. I think the water company must've done some sort of treatment or something. I also assume that the normal cycle has now stalled due to low pH, given the rising ammonia.
 
Anyway, I'm in a bit of a panic about what to do - I know I can't raise the pH quickly, since the fish are probably already in shock (I noticed the glowlights barely eating this morning). I just checked the tap water pH and it's gone up slightly to 5.5ish....I guess it's going back to normal slowly. Is there anything I can do in the meantime to save my fish??  
 
 

 

[rossyk]

I should add - our water is pretty soft (only 18mg CaCl/L), according to the local water company, so that explains the usual tap water pH of around 6.5.

 

[snazy]

That's strange because a 25% water change shouldn't be able to bring the Ph so low. (25% water with 5ppm Ph mixed with 75% 6.5ppm Ph would roughly make a Ph of 6.13ppm, not 5ppm)
My guess is the Ph has been dropping all along in the tank and you only noticed/associated with the water change. Soft water, once added to the tank, due to a lot of acidifying processes will go even softer and if yours doesn't have much buffers to hold the Ph, it will be crashing. I think you'd be better off with some crushed coral in the filter(add small amounts slowly as to not raise it too much) to keep the Ph buffered.
My tap water straight out the tap is about 6.6. Once it settles for 24 hours it goes up to 7.4-7.6 and stays there in all tanks. So it's worth testing your tap water once it sits in a glass or similar for 24 hours. This will give you the "real" tap water.
Either way, you are right that at Ph of 5 there's no bacterial living in the filter. Raising it now is dangerous as the tank needs to cycle again and the higher the ph, the higher the NH3 ammonia, but you need to do it with lots of small water changes to keep the ammonia down and raising in the process the Ph with other means. It's possible that the tap water itself will provide enough buffers to raise it back up to 6.5 but that means very regular and larger water changes on permanent basis, otherwise crushed coral.

 

[RossC]

I wouldn't suggest trying to raise your pH as it normally does more harm than good. I thinks going to have to be a case of getting the fish used to the new pH as its what your going to be using in the future. The cycling is a bit of an issue though. If you don't notice a drop in your ammonia within the next 24hrs I'd recommend maybe asking a friend or a local fish store to house your fish until the filter has cycled back to 0ppm ammonia

 

[rossyk]

Ok thanks guys. I did a partial water change (the tap water seems to have normalised back to around pH 6.5) and the pH has risen very slightly and ammonia is now at 0. The glowlights seem happier and the shrimps have emerged from hiding (haven't seen 3/4 of them for about 3 days). The corys seem ok, but I'm not overly confident of observing their normal behaviour since I haven't had them very long. They seems to be spending a lot of time going from top to bottom, rather than foraging on the bottom. I have a bad feeling that they might be casualties in the near future.
I'll nip to the LFS and see if they have crushed coral, although I have a slim filter and have no room for it inside. Would it work suspended in a bag in the tank? Or would perhaps a limestone decorative rock from the LFS do the same trick?

 

[snazy]

You can't keep these fish and shrimp at Ph of 5. They'll die. You need to keep it buffered to above 6 somehow, but careful with crushed coral or such as it can raise it too high if you put too much at once. You can try a rock of somekind, a dead coral,  etc.. and keep measuring the Ph. If your water is too soft as it seems, it may just balance it out back to 6.5 for good but it depends. The shrimp need some calcium supplement as they'll die molting and your water may not have enough or much at all.
There's no nitrification going on at a Ph of 5ppm as far as I know. The bacteria in our tanks gets inhibited at a Ph of 6ppm and below. There maybe some different form of nitrification at such low Ph, I am not sure but certainly the ammonia is probably non-toxic at this stage so it doesn't matter. You may as well throw your filter out if you'e got a ph of 5, just a powerhead for the surface movement.

 

[rossyk]

Thanks leader. My pH at the moment seems to be around 6, mostly due to the tap water returning to normal before the last water change. I'll check it again in the morning and do another partial change to slowly bring the pH back up to normal.
The LFS didn't have any crushed coral, so that won't be an issue. The calcium supplement is a good idea - I got a water hardness test today an apparently the calcium content (KH?) is rock bottom, while the GH is ok. That may explain why I haven't seen 2 of the shrimp in days....