Ph swing during fish less cycle

[Justin Taylor]

During cycling without fish in one day my ph went from 7.6 (which is the level it comes out on my well) down to 6. I had just added the normal ammonia amount that day. What would cause that?

[Vlad Jovanovic]

If the test result is correct...the nitrification process itself will acidify your water. That is why people have to regularly add a pH buffer (alkaline/base) of some sort to raise pH. (Lime, potassium hydroxide, potassium bi-carbonate, calcium carbonate, potassium carbonate or more "hard" high pH top up water etc...) It seems like maybe the buffering capacity of your water has finally been used up. (Most well water with a 'high' pH seems to have a lot of calcium carbonate, or more correctly calcium bicarbonate in it...to oxidize 1mg of NH4 into NO3 the bacteria consume somewhere in the neighborhood of 8mg of carbonate alkalinity and about 4,5mg of Oxygen. Now that your done cycling and your bio-filter is clicking away nicely, they've used up all that fuel and you need to add more...

If you use a API Master test kit and it only goes to pH 6...you should take action to raise your pH, since below that reading you really have no idea of what your actual pH is...it could be 6 or it could be 5.5 or whatever...you have no way of knowing.

If you don't take steps to raise your pH your bio-filter will eventually crash...

[TCLynx]

Justin,

What Vlad Says is correct.

   First, if your water right out of the tap tests at a pH of 7.6, it could actually be much higher than that.  If 7.6 is the pH after you have let the CO2 outgas then fine.

Anyway, How long had you been cycling when the system pH did this drop in 24 hours?  This is not really that strange.  I have observed something similar when I cycled up my first system.  Along about the time the nitrite spike finally dropped, the pH dropped too from up in the high 7 down to 7 and then down below 6.5 in about 3 days time and I added some egg shells but it kept dropping to almost 6 when I finally added a spoon full of garden lime.  Now I've learned that simply topping up with some well water occasionally for the calcium carbonate and using rain water and potassium bicarbonate will usually work for my particular location.

Yes it is the bacteria causing the pH to drop and this is natural if if for some reason your pH starts climbing instead, it might be time to look for anaerobic pockets that need cleaning or some other explanation for it (like a leak causing too much automatic topping up from hard well water.)