I know there are different opinions on this, but I am concerned that I am out of balance.

My system:

75 gallon tank with T-5 lighting, a CPR RR bak pak skimmer (smaller than it should be--I bought it originally for my 30 gal. Rated up to 60 I think), and a couple of powerheads (probably around 1000 gph of flow total). At the moment I am using Seachem Reef Salt (I may be switching soon).

Inhabitants:

Foxface Lo
2 Occ Clowns
1 Clark clown
1 Coral Beauty
1 yellow watchman
1 mandarin
1 lawnmower blenny
2 cleaner shrimp
various snails and crabs

Some soft corals

I usually feed once per day (one cube of mysis plus a large pinch of formula 2 flakes). I also add a squirt of phyto and zooplankton every 2-3 days (probably about 1 Tablespoon each). Everyone seems pretty happy, but I am having nitrate woes and some diatom dusting/cyno. Is this too much food? How do I know how much is too much vs. too little?