I experienced this awful mess last fall so I keep this list of tips that helped me. This is a prior response:
"I this Dinoflaggellate problem also a couple months ago. It was a light brown/tan mat of slime, with tons of tiny air bubles, covering substrate and glass. It formed long goopy strands. It blew off the rock easily. It was way worse at 6 p.m. and would seem to subside overnight, but return with a vengeance every evening. It would cover things in a matter of minutes. Sound familiar?
In my case PH would rise every evening to 8.6 evening, but I also had low alkalinity (High ph was probably caused by the daytime photosynthesis of the bloom (ie, lower CO2, higher Oxygen). Surprisingly nitrate had consistently tested very low on Salifert.
My tank was six months old, 75g, open tank, 175w mh (5.5k) with actinics, no sump, 80lbs
live rock, and 4" aragonite "sand" bed, no plenum. Very little life in the "sand" as I
seeded it with on 3-4 lbs live sand because I thought live rock would seed it over time.
I thought a CPR bakpak would be enough given light bioload and 80 lbs live rock.
Anyway - there is the background and hear is what I did to finally lick this problem. I
listed them in a possible order or importance in my case.
1. I upgraded my skimmer from the weak CPR Bakpak to a Turboflotor 1000 HO from Aqua Medic. Better skimming was very important.
2. Simple water changes and blowing it off the substrate (rock, sand, and glass) were
not enough. Water changes are important, but I finally got wise and did direct siphoning
of this gunk off the substrate with a 1/2" tube. Siphon the junk out of your tank into a
bucket. Don't just swish or blow the stuff around in the tank or simply do a water change - You need to suck this stuff out!. This also was very important.
3. I boosted alkalinity to recommended levels and resumed dosing kalk. I had made the rookie mistake of stopping kalk and alkalinity maintenance for fear my ph would keep rising beyond 8.6.
4. Use activated carbon. I used Kent at first and then switched to Two Little Fishies
Hydrocarbon II - probably doesn't matter which one though. I used a little Kent
Phosphate Sponge also.
5. I used a temporary mechanical filter (Aquaclear 300) to filter out the gunk which was stirred up and/or suspended in the water column.
6. I cut the photoperiod back on 175w mh to 4 hours a day.
7. I cut back on feeding a little.
8. I drank booze and prayed for patience.
These worked for me and my tank finally cleared up - crystal clear. I have since added a sump and a new improved sand bed, but these came after the problem had already
started cleared.
I think adequate skimming and direct siphoning of the gunk out of the tank were the key. I also believe that a truly live sand bed would have helped avoid this problem (Dead aragonite "sand" bed was a detritus trap)."
Good Luck!
