There should be varying amounts of Nitrate even in fully cycled tanks.
Plants DO reduce Nitrate, but I notice tank three on your list doesn't have
any plants?

Do you do regular waterchanges? Depending how often and how much water you
change, you may see only small amount of Nitrate.

Clive

No plants in tank 3 because it is temporary for the eels, and eels
*dig* I tell you! I don't think plants would do well with the eels
always digging them up. I know eels require a much bigger tank and I
hope to accommodate them with a bigger tank within a few months. I may
add plants to tank 3 after the eels are moved out. It may then become a
fry nursery if needed for the platys or guppys.
As for water changes, I do a minimum of one 30% weekly water change and
gravel vac on all three tanks. Sometimes I do an extra 30% water change
mid week. Most of the fish seem to love the water changes.
Tanks 1 and 3 have penguin biowheel filters and tank 2 has an older back
hang-on filter and a UGF. I prefer the biowheels.
I also forgot to mention that there is driftwood in tanks 1 and 2, and
there is a coconut shell cave in each of tanks 1 and 3. One of the eels
has taken up residence in the coconut shell and only digs in the
substrate occasionally. The other eel just digs in the substrate and
ignores the coconut.


Karen