Help think i have Dinoflagellates

[spider8u]

Hi i think i have Dinoflagellates in my tank or it could be Diatoms really not sure. I have brown algae on the sand the rocks and the glass but there is also air bubbles where the brown algae is now i have had Diatoms before when i first set up my tank and i don't remember seeing air bubbles in the algae. My tank has been set up for a year now. This all started about 2 weeks ago after i changed my T5 bulbs for new ones. I have been doing 20gl water changes ever week using RO/DI water i have been trying to siphon as much of the sand as i can but the next day it all comes back. I have cut back my lights from 8hrs a day to 4hrs maybe i should turn them of for a day or two not sure. right now i am using a canister filter and a HOB skimmer and using 2 #3 Koralias for flow. In the canister i have a put some Carbon and PhosBan media in there but that don't seem to be doing much. I will be setting up a 20gl sump just waiting on the skimmer and HOB overflow but for right now not sure what to do just did some tests on my water this is what i get

SG 1.025
pH 8.3
Alkalinity 10.2
Ammonia 0
Nitrite 0
Nitrate 20 seems its always at 20 even after i do a water change
Calcium 450
Phosphate i am using a Salifert test kit and it comes up yellow

[papagimp]

I've heard through the grapvine that salifert makes a pretty shotty phosphate test kit. The others all get great reviews but just these for some reason i hear bad things. Also, nitrates are probably helping to fuel the diatoms/dino's whichever you're experiencing. I've never witnessed my diatom blooms getting air bubbles either, but any algae/plant for that matter that is doing well and thriving can pearl up bubbles like that.

I would imagine that syphoning the sanbed would promote more diatoms to grow. Your not removing the "fuel" for the algae, just the algae, so naturally more will grow where the rest was removed. Something in the system is fueling this stuff, and it probably does have something to do with the new bulbs. I'm seeing the same thing in my tank since this last weekend when i replaced 2 out of 6 of my bulbs (t5 54w aquablue +'s). fwiw, I've got the 2 x #3's as well running, this is a 75g I'm dealing with, and the girlfriends 75g which is plumbed into the same sump, does not have these problems. Lighting and flow are the only differences in the tanks.

[spider8u]

Looking for some more info

[papagimp]

maybe dim the lights down to 4-6 hours a day for a few, or cut em for 3 days straight, then acclimate them to full 10 hours or so. Run some phosphate remover, stop syphoning out the sandbed, but keep the algae off the corals. Get that skimmer and sump going ASAP, a macro filled refugium wouldn't hurt either.