"Cardman" wrote in message
...

BTW -- you should try to get those nitrate levels down. 100ppm is
definitely on the very high side where it will be toxic for at least some
fish species.

My fish can live in much higher levels perfectly fine, where they just
become unhappy in a world where algae rules. So they are very happy
with anything between 50 and 150 mg/l, when algae growth is very slow
at this level.

100 ppm NO3 is extremely toxic for freshwater fish, but of course any animal
can acclimatize to unsavoury conditions given time. I'm not surprised that
algae growth is slow at 100 ppm Nitrates. Algae is opportunistic and will
find a better environment or hibernate.

Adding lots more plants will help in reducing nitrate
levels.

A nice idea, but what you do not mention is that plants in fact use up
very little Nitrate, which is why I would have to bed plants very
heavily for any beneficial effects.

Plants use a lot of NO3 here. Given that your nitrate levels exceed 100ppm
I'm not surprised that you see no NO3 consumption.
The poor plants have no chance to even get started.

I'd suggest you reduce nitrate from your tap water to start with.

Regards
Graham.