HELP!! EMERGENCY!! Diatom problem


New member
I need help bad!!! For the last 2 months I've been battling what I believe is Diatom algae (pictures below). I can't seem to make it go away. Up until the last couple of weeks my coral has still been happy and growing, but now they seem unhealthy and some have even bleached and died. The corals I have lost are a green slimer, bubble coral, a favia, and two chalices. Some corals that seem unhealthy are all 3 of my frog spawns (pictured), my torch coral (pictured), and my monticaps. The frog spawns and torch coral do not open up all the way and the monticaps have started bleaching. They have been this way for a week. However my maxima clam, inverts, and fish all all doing fine. I need help getting rid of this. Does anyone know whats wrong with my tank? Below is a complete live stock list of my tank and all the information about the water and set up. I'll try and give as much info as possible.

Fish: Hippo tang, yellow tang,2 orcelaris clowns, dragonet mandrin, 2 chromis
Inverts: 8 blue leg hermits, 5 red leg, 10 astrea snails, 1 serpent star, 1 emerald crab, 1 maxima clam

Coral: 3 frogspawn, 2 monticaps, 1 hammer coral, several zoa's, one brain coral, one acan, mushroom coral, one birdsnest, 1 torch, one leather toadstool.

System: 75 gallon tank with a 29 gallon sump/ refugium, protein skimmer, 2 powerheads, 110lbs of live rock, 120lbs live sand
Lighting: Light fixture with 2x 150watt MH, 4x 65watt PC act.

Dosing: purple up when calcium is needed and kent phbuff for alk.

Water Quality:
Calcium- 425
Phosphate: .1 ppm
pH: 8.4
Nitrate: 0ppm
Ammonia: 0ppm
Salinity: 1.023
Water temp: constant at 80*F

Things I've tried:
Vacuuming it out, many times
3, 15% water changes
20% water change and adding the 29g sump

Does anyone know what could be killing my corals and causing the diatom algae?? How can I get rid of the diatom algae?? Is there a liquid additive that will kill diatoms that is reef safe??
Any help will be greatly appreciated!




New member
BTW it looks like cyano algae.May try like a 50% water change.Chemipure elite and purigen.if all else fails may try peroxide dosing or maricyn (erythromyacin)


New member
its maracyn i think its in red slime remover.Did you remove all ur carbon chemipure etc,Did you do it for the full 7 days?May look into hydrogen peroxide dosing .Gigantic thread about it on RC.


New member
Have the store test the TDS of their RO/DI in front of you. Many stores sell water from units they haven't changed the filters in forever on. I've noticed silicate fed diatom blooms when my RO/DI was reading 2ppm which was cured with replacing the filters and doing a 3 day lights out period.

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New member
i'm not sure it's diatoms looking at the pic.u should get ur own ro/di besides knowing ur water quality it's a lot more convenient.blacking out won't hurt for sure.


New member
It looks like it might be dinoflagellates to me, either way, are you running GFO and carbon? That will remove any phosphate and silicates in the water. .1 ppm is high enough to cause algae problems. Also, check your source water for phosphates and tds. That is probably the root of your problem, although you still need to run GFO and Carbon to get rid of what is there.
Also, make sure you are not running those lights too long. On that size tank running lights for more that 9 or 10 hours total you will have algae no matter what. Look into doing a couple days black out too. I have almost the exact same lighting on the same size tank and run my halides for only 7 hours and my actinics for an hour before and after.


New member
do 10 percent water change each week for 6 weeks. check into the water you are buying. it looks like bad water to me.


New member
Thanks all for helping. I think im going to buy my own RO/DI unit and do a 50% water change, following up with a 10% change each week until I notice a difference. I was checking out another thread and they said something about old bulbs may be affecting it too? This would make sense because I bought that light used and the bulbs could be worn out. Let me know what you think.

Also, anyone know how I could quickly perk up the coral, I'd hate to lose them and I'm worried about doing a total black out while they look so bad