Ross Vandegrift wrote in
m:

Hello everyone,

My 20Gal long tank, with 2wpg, had something happen to it a few
months ago. My plants stopped growing well.

IT sounds like you havea 20W bulb on there. Standard flourescent bulbs last
6-12 months before output drops significantly. This is the most obvious
thing to check.

but I did the obvious things as the
plants slowly died off - stopped dosing fertilizer so much and cut down
the light.

Cutting down light is never a cure for anything, unless you have too much
light. Even if your bulb were new, this is not your problem. Turn it back
on 12 hours per day.

The symptom of too much nutrients is algae. You do not have that symptom,
so too much ferts is not the problem.


I change 3-4
gallons on a monthly basis. And this tank, exactly as I'm running it
now, was previously very, very successful.

This is a classic case: Originally your tap water had sufficient nutrients
for some plants, so they did well. Since you change so little water, you
replaced very little, and eventually something ran out (probably Potassium,
or if your tap water is soft, Calcium or Magnesium, although I don't know
what you dose.)

Replace your bulb, change 25% or more water per week, watch your plants
jump to attention.



I thought that perhaps the tank had been contaminated, but this
seems unlikely

Yes, very unlikely.