Looking for Help on Coral's Demise

[reddogf5]

I would appreciate any thoughts regarding a few questions on my aquarium.
It is a 28 gallon nanocube, compact fluorescent.
It has been set up since January '10.
After the initial cycle, ammonia, nitrites, and nitrates have been at zero. The other parameters are typically as follows:
pH 8.1
Alk 3.0 meq
Calcium 440 ppm
Mg 1275
Phosphate 0.1 (could never get it to go to zero)
Salinity 1.025-6`

I want to find out what corals I can keep, and what the failures are due to.
These are the corals that are thriving:
Gorgonian
Mushrooms
Xenia

Things that did OK for a while:
Favid
Millepora (1 expired quickly, one thrived for months)
Montipora (plate doubled in diameter)

Things that did not do well:
Bubble
Hammer
Frogspawn
All wasted away

I wasn't diligent on testing because things were pretty stable in about September. In November,
Mag dipped to about 1200 ppm
Alk drifted to about 2.0 meq
Phosphate climbed to about 0.5 ppm
The next week nitrites spiked to about 0.2, as did nitrates. No ammonia, though.
At this point, two monti frags and the remaining milli frag expired in a pretty rapid fashion.

Any ideas why the Euphylliidae (bubble/frogspawn/hammer) melt away? The bubble was the first, and lasted the longest. The hammer expired faster, and the frogspawn went down hill even faster. Could it be due to the presence of the xenia, mushrooms, and gorgonian, or something else?

Any thoughts on the sudden demise of the montis and milles? Caused by the shift in water parameters, or due to the presence of the xenia, mushrooms, and gorgonian?

My goal is to figure out whether I am doing something wrong, or if there are some things I just can't keep in this set up.

Thanks.

[Agu]

First of all I'm not a fan of having a mixed reef in a nano tank.

Too much chemical warfare and not enough dilution. Also different corals need different flow/lighting and that's hard to do in a nano tank. Finally the intensity of flow/lighting isn't defined.

The weeds that survived can live in anything. The SPS need high flow and high light. The euphyllia need medium flow and medium light. You're trying to grow too many different kinds of corals in the confines of a 28 gallon tank imo.

That's just my opinion and doesn't address your chemistry questions because other then temp and specific gravity, I haven't tested anything else in my tanks for years. For me chemistry is taken care of with water changes and coral health is maintained by creating the appropriate environment.