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Dinoflagellates in Fluval 13.5

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Hello fellow reefers!


Like many of you, I have a problem with dinoflagellates in my Fluval 13.5 (almost stock everything with the crappy skimmer)--so much that I gave up trying to control it about 3 months ago (after a 3 month battle) and basically just physically remove it when I have people coming over. I now have a renewed inspiration after setting up my planted tank in my office.



1. Bristle worms got huge and more numerous. I think of them now as carnivorous feather dusters that move around.

2. My ocellaris and clown goby don't seem to be bothered.

3. My zoa colony population got wiped out (2% survivors currently likely).

4. My maxima clam is thriving (5" now--got him two years ago at 3").

5. Mushrooms/LPS/toadstool corals not hurting, but not growing/splitting. (toadstool needs a scrubbing on it's top with a toothbrush every now and then)


Before you ask, here are some common clarifying questions/answers:

1. Water parameters/water changes? --Haven't tested in 3 months and last changed the water a month ago (please hold judgement, I gave up)

2. There are >1000 species of marine dino, have you ID'ed the type of dino? --Haven't used a microscope, but it makes bubbles and it's apparently non-toxic as it hasn't killed anything to my knowledge [with toxins]. Not sure how I'd ID the actual species

3. Do you dose? --No, but I tried baking powder/vodka to no avail


My Questions:

1. Does anyone have experience with UV working on dino? I know this is more for species that live in the water column and I have no idea if mine is this type. I can post photos if it'd help.

2. I'm up to try a blackout--will my clam likely be able to survive this and is 3 days the recommended? Should I do this before or after a water change [and physical removal] or does it not matter?

3. I've read a hydrogen peroxide... won't this kill everything?

4. If I wanted to nuke the system and start over, is there any way to save the existing corals/livestock without reintroducing the dreading dino? I love my two little fishies and my clam [corrals are meh at this point, but I'd prefer to save them].


Thank you!

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Euphylin me

dinos can be very tricky and different species require a different approach. hydrogen peroxide wont kill anything in the recommended dosages (although it may irritate some corals and your clam). i would put the clam and clowns in a small holding tank. do a 20 percent water change, 3 day black out, 20 percent water change and then run phosguard/ gfo as some dinos feed off of silicates. some are photosynthetic...i hope this helps! i would try peroxide as a last resort

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UPDATE--I think I might've beat it (wish I took photos before and after)!


I put a bunch of chaeto to suck up any spare nutrients, added another small power-head for increased flow, and finished up the final try with a 4 day blackout (because I was conveniently at a wedding for 4 days last weekend). I didn't remove the clam/clown/goby because I was worried I'd reintroduce if it somehow hitchhiked (not sure that's possible: they all seem healthy now. I did the next two days with actinics only and followed that with a 40% water change/media & pump rinsing. Salinity was also really high (1.029ish) when I beat it because of a lack of top offs on my part--not sure if that helped/hurt. Good luck to anyone else fighting dinos. I'll keep you guys updated if they come back.


Thanks for the tip on Phosguard, Euphylin, I'll be sure to use it if they seem like their coming back.

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My previous tank got wiped because of dinos.

Best of luck ! 

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Still hanging in there?


If possible, can you get your water tested?   LFS will often do it for little-to-nothing.   NO3 and PO4 in particular, but all the basics are usually interesting.


FYI there aren't really that many species of dino that we'd have to be concerned with, and you can see them with any scope.  There are a ton of ID pictures floating around on the reef-web....I've got a 5000+ long dino-post (elsewhere😐) with a ton of ID photos all by itself.


Check out the Dinoflagellates section of my blog for general research on them if interested.  It's stuff that more or less directly applies to blooms in our tanks.  (There are a few non-pest dino articles in there....most are on the pest variety.)

Some of the best:


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