Sudden Ph Drop. Possible Reasons?

[JSmails]

Ive had a sudden PH drop in an established tank from 7 down to somewehere between 5 and 5.5. Now what could have caused this? Any of these?:

1) I had a cory die and I couldnt find it for nearly 2 weeks, eventually the skeleton turned up so that could be one reason?

2) I have recently added a few rocks and slates but wouldnt this more likely cause a rise?

3) I used Nutra Feed to help plant growth, could this cause it?

4) There was a build up of waste food, when I had been on holiday, which is now removed.

 

[Xraymark]

The increase Is problably due to increase of waste food. As it decomposes the ph can drop.
Watch your ammonia as the filter bacteria might go dormant with the low ph. I assume you have done a water change to bring it back up.

 

[Essjay]

The food would have composed to make ammonia which your filter would have processed to nitrate. This is acidic and lowers the pH. But that is a rather large drop in pH for a bit of uneaten food.
Do you know what your KH is? If it is very low, there would be very little buffer in the water, and it wouldn't take much added acidity to drop the pH a lot. If you have been on holiday, does that mean there were fewer water changes than usual? With low KH, regular water changes keep the carbonate topped up. My KH is between 3 and 4 and I suffered a pH drop a few years ago when I got a bit lazy about doing water changes Since I've been doing weekly water changes without fail, it hasn't happened again.

 

[JSmails]

The food would have composed to make ammonia which your filter would have processed to nitrate. This is acidic and lowers the pH. But that is a rather large drop in pH for a bit of uneaten food.
Do you know what your KH is? If it is very low, there would be very little buffer in the water, and it wouldn't take much added acidity to drop the pH a lot. If you have been on holiday, does that mean there were fewer water changes than usual? With low KH, regular water changes keep the carbonate topped up. My KH is between 3 and 4 and I suffered a pH drop a few years ago when I got a bit lazy about doing water changes Since I've been doing weekly water changes without fail, it hasn't happened again.

Just tested and my KH is around 2. So thats allowing it to happen isnt it? Is there no way of increasing the KH or is that just the way my tap water is?

Ammonia test was fine, Nitrates were slightly higher than normal.

OK this is good thanks for the answers so far. Excess food has gone from ammonia to nitrates and lowered the ph. I'm sure the rotting fish wont have helped too.

Yes I did a water change today and brought it up to 6.25. Ill increase it again over the weekend.

 

[Essjay]

That KH is rather low!
One way to increase it, albeit slowly, is to add some calcium carbonate to the tank. This could be in the form of limestone rock, a pieces of coral, shells, or a bag of crushed coral in your filter. Calcium carbonate dissolves slowly, increasing both KH and GH a bit. This may be enough to stabilise your pH.

 

[KittyKat]

What is the tap water KH?

The best thing to do is to do small water changes, like 10% per day, until the pH is back up again. A large water change will make the water hardness/pH change too fast, which can be fatal to the fish, so it is always better to make sure these changes happen slowly.

On a side note… why was there a food waste build-up if you were away? I would expect no food at all when I leave, as I do not usually have my fish fed, or the same amount of food as normal, as I would pre-pack the food for anyone else feeding them.

 

[reignofcheese]

ammonia as the filter bacteria might go dormant with the low ph

The good news is ammonia goes nontoxic at low pH anyway

keep the water changes small, the less sudden pH shift, the better for the fish. keep an eye on those levels, if it drops again even with regular water changes You'll need to buffer it.

 

[JSmails]

That KH is rather low!
One way to increase it, albeit slowly, is to add some calcium carbonate to the tank. This could be in the form of limestone rock, a pieces of coral, shells, or a bag of crushed coral in your filter. Calcium carbonate dissolves slowly, increasing both KH and GH a bit. This may be enough to stabilise your pH.

Thanks for your help on this. I'm on top of what I need to do now. Ive added some crushed shells in a bag in the filter. Hopefully I can slowly bring it back up. Unfortunately it is an issue with the tap water.