A few months ago I shut down the UGF system in my 500L display tank in
order to experiment with the addition of phosphate pellets to the
substrate. The UGF consisted of two undergravel plates, each
connected by a lift tube to a powerhead. The lift tubes were removed
from the tank leaving the plates in place. The powerheads, no longer
connected to anything, were left in the tank for circulation. I shut
down the plates one week apart to minimize the expected shock to the
biofilter. After the second plate was shut down, the tank water
became slightly cloudy for about two weeks, but neither the plants nor
the fish seemed to object.
After the water cleared up, I began burying phosphate pellets (Vigoro
Triple Phosphate 0-48-0, available at any garden supply store) deep in
the substrate at the rate of about one 3mm pellet per 50L tank water
every couple of months. There has been a very postive effect on the
growth of many of the plants, most notably the E. tenellus (which is
now spreading aggressively) and the formerly tiny N. lotus. The
crypts don't seem to be affected much one way or the other, except for
the formerly invasive C. walkeri and C. petchii, which are spreading
much more slowly now. I suspect that these two crypts were partial to
the circulation provided by the UGF. The water has developed a slight
greenish tinge, noticeable only when viewing a white wall through the
tank's long dimension (6'). There's also a little more green-spot
algae than I like on the older leaves.
It occurred to me later that I'd missed an excellent opportunity to try
a plenum design (discussed long ago here in APD) in which nutrients are
added to the tank from below the substrate. Oh well.
Kevin Conlin Montreal, Canada "We're Canadians. We HAVE to be polite"
Finger as332 at freenet_carleton.ca for PGP public key.