I have a heavily stocked, moderately well planted 20 gallon tank. It is filled with guppies, 1 hillstream loach, 1 dwarf gourami and some amanos. This tank is 5 years old and quite stable. Typically parameters look like:
pH 7.4
GH 8
KH 4
Ammonia 0
Nitrite 0
Nitrate 40-70ppm
I just came back from vacation and wanted to see how the nitrates were looking as that is the parameter I am usually chasing with water changes. To my surprise my pH and KH have both crashed. Current parameters are:
pH 6.5
GH 11
KH 0
Ammonia 0
Nitrite 0
Nitrate 65ppm
I have no idea what has happened. Fish from what I can tell all look fine. Some plants are looking not great but not sure if related: crypt wendtii with a bunch of pale yellow leaves, java fern and anubius have multiple leaves with holes with black edges around them.
I had our pet sitter add a pinch of my usual flake food every day while I was gone. Quite possible she overfed as she completely fouled up my other tank. The only other thing I did differently was add a Zoo Med Nano block for my amano shrimp. I would assume the nano block would have had the opposite effect on my KH/pH though.
In case it is relevant I also have a small bag of API Nitra-Zorb in the filter to help control the nitrates but I have been running this on and off for months. I did recharge the bag right before I left.
Any ideas why this could have happened? Also how do I deal with this? Water change seems obvious but do I have to do so cautiously to avoid a pH shock to the fish?
Any advice appreciated!!