I typically do a 25% water change on all my tanks once every 8 or 9 days. This keeps my nitrates in all 4 tanks at 5 ppm. Once, in the summer when we were doing a lot of camping, we went 19 days between water changes. One of the tanks was at 20 ppm nitrates because of the delay. Ammonia and nitrites are always zero. (When we kept goldfish, we would occasionally get trace amounts of ammonia in that tank, but we don't keep goldfish anymore)
That's the highest my nitrates ever got, 20 ppm. And just the once.
So I was quite alarmed on Thursday when we tested the water on my 55 gallon Silver Dollar tank and it showed 80 ppm nitrates. It had been a week since the last water change.
Now, I had a peacock eel die this week, and he used to hide regularly. So it's possible he was dead for a day or two before I lifted his hiding place and discovered he was dead. I thought this is why the nitrates were high.
So Friday I did my usual 25% water change. Today I tested the water, and the nitrates are still 80 ppm!
This is quite a jump from the usual 5ppm so I am alarmed.
I have no plants in that aquarium, as it is a silver dollar tank. But even without plants, until now my nitrates have always been consistent.
This is what is in the tank:
4 x Silver Dollars (6")
1 x Hillstream Loach
1 x African Dwarf Frog
5 x Serpae Tetras
4 x Mollies
1 x Leopard Bush Fish (2")
1 x Pearl Gourami (2.5")
TEMPORARY: 5 Bala Sharks (2.5")
A couple of weeks ago we added the 4th Silver Dollar. I can't see how one fish could result in my nitrates being 15 times higher than usual.
So anyway, what should I do? Should I just start doing larger water changes on that tank, like change a third of the water instead of a quarter?
Could this be because I have been feeding blood worms a little more regularly? Could I be over feeding? Would that cause my nitrates to spike?