what's causing the green water?

[Don E]

I had a terrible greenwater problem with my first tank. Tried carbon, tried phosphate sponge, even tried rotifers which are supposed to be able to eliminate an entire pond of greenwater in days, but nothing worked. It went on for two months. Finally, as a last resort, I did a 100% water change, which in retrospect was a little too radical...

Anyway I discovered that I had had a couple of turbo snails die and foul the water, and the nitrate spike caused the green water. The spike never registered on my tests as the nitrate was converted to very aggressive phytoplankton instantly.

After the water change, no more problem. But the water change killed a couple of my inhabitants.

I did some reading after that- apparently with a huge spike in your nitrogen cycle, you can get the greenwater before the spike really registers.