Something in going on in my tank?

[b_james]

I cant figure out whats going on with my tank, First off, Im having this problem with golden/brown diatoms that wont go away - its getting worse and worse. even an hour afer stiring up the gravel pathes start to form. In heavier areas the diatoms develop small bubbles on the surface wich are eventually released and float to the top. In the last couple of weeks I have lost 4 chromis and both my cleaner shrimp (the last one perrished yesterday - looked like he just fell off a rock). All other live stock are is great shape - all are very health, good coloring on no unusual behavior. All corals look healthy, open and growing well. There is absolutly no agae on rocks, no hair agae no slime just a light green dusting the glass every few days. BUT the sand gets covered within hours of the lights turning on and is now starting to cover rocks and corals with a light golden brown dusting that easily blows off.

all Coralife MH & actinic bulbs are less than 2 months old (new unit)

PH 8.4 (test kit ran out so I used my hot tub tester)
Nitrate 0 (According to the color chart) (maco algae popluation decreasing)
phosphate 0
Amonia 0
All water from initial startup is RO-DI - resin cartridge replaced about a month ago is a Hi-S resin.
Instant Ocean Salt.

Any Ideas???