Diagnose slow decline

[syncro]

Bulbs: 350w total of 10K MH and actinic T5 about 16" above surface
CUC: 1 hermit, 2x zombie snails, bristle worms, spaghetti worms and unfortunately flatworms.
Water params: ammonia 0, nitrite 0, nitrate 0, phosphates 0, salinity 35ppt, temp 24.3-24.7*C, aquavitro salinity mix

CUC is probably too small now. I'll add more.

Another vote for the "too clean" theory, thanks Hazratty. I'll sell the haddoni (too demanding) then experiment with running less clean. On one hand, I am putting far more food into the system than I was before this decline. On the other, before the decline I was doing water changes once a month or less with the minimal bioload. In any case, I think it is worth experimenting with.

Titus, it could be diatoms. A quick search sounds like diatoms are brown and cyano is red. I'd guess this algae is more red than brown. If diatoms, let them run its course. If cyano, then nutrient problem?