Join Date: Jun 2014
Location: Cape Coral, Florida
Why are nitrates accumulating faster now?
I have a fully cycled 45G low tech tank that has been getting increased plants (the jungle val is going nuts), and decreased fish.
Originally I had 5 congo tetras, 5 serpae tetra, 1 BN pleco, 1 Raphael catfish, two angels, about a dozen ghost shrimp and some snails.
I would go about 3-4 weeks between water changes taking it from around 20 down to 10-15 or so. Then it would slowly accumulate again.
I took out the 5 congos to put with a school in a big tank, and 2 serpae died (for reasons unknown but I think unrelated). They were removed on their last days, they did not actually decompose in the tank.
For the last 2 months or so I've had to change water far more aggressively, like 4 times as often, to keep nitrates down.
I have not changed fertilizer routines with one exception. I dose with 5ml comprehensive weekly, 5ml iron and excel daily, and 5 ml potassium weekly if I haven't changed water (which is RODI with Equilibrium which is heavy potassium).
The one exception is I am starting to add Phosphate to get it to detectable levels and combat a very mild case of green spot algae, which is indeed helping. It is currently at .2 ppm, with 2-3ml daily of seachem (all of these are seachem or equivalent).
So why are nitrates accumulating faster, when my plant mass is probably 50% greater than it was when I was doing less, and the fish load is substantially less as well?
Does something happen in the substrate (ecco complete + gravel), that reaches some steady state then stops consuming nitrates? Or starts producing more?
Note that I do not think it is measurement error. I have another large tank that I use the same kit, and that tank is also very lightly stocked, moderately planted, and the nitrates are steady or going down (today they show 5ppm -- I'm worried I may have to start dosing N soon).
I expected this small tank to behave similarly, but instead for a couple months now, it has been churning out nitrates like crazy.
Can phosphate addition trigger some process that might be responsible?
Is there some other process that is at work?
This isn't a big deal -- I can just change water more often if needed (and please, can we avoid the idea there is some magic number and frequency). But I want to understand why it is happening.
When I removed 7 of 14 fish, I really expected the nitrate production to go down, maybe even drop (due to plant uptake). But it's at least 3-4 times the rate it was. Why?
Latest tank build:
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