Diatom bloom on macroalgae


In Memoriam
I have a fuge with mixed macroalgaes, including 2 strains of chaeto and some 3-4 caulerpa sp.

There is a (brown) diatom bloom, and it is growing on top of the algae. How do I make it g away?

It has not started to spread to my display's walls. I read about shutting off h lights for a day or so every week so i have tried that beggining today, but what else can I do?


Premium Member
Blow it off with a turkey baster and hope the skimmer removes it.

Or remove the chaeto after a waterchange and swish it in the waterchange water.


Cancer Sucks
Leave it alone, IMHO. It's a fuge. Whatever grows in there is taking away from what can grow in the main tank. If you stop the diatoms from growing in the fuge, they'll take hold in the main tank.

Agu's second suggestion is good too.

BTW, my chaeto grows great with and without diatoms growing on it. (and a little cyano :lol: ) (but, the cyano stays out of the main tank)



In Memoriam
That's my problem right there. it is outcomepting my macroalgaes and they have stopped growing. I like fast growing caulerpa so my tang has some natura food to feed on.

And macro is a lot easier to harvest.


New member
UV will not help with diatoms or cyano.
You can take the chaeto out and rinse it regularly even in tap water (I do it once every two weeks).
Diatoms, if they are really becoming a nuisance check your water purification. Silicates will promote Diatoms.


Cancer Sucks
I still say let the diatoms flourish in your fuge. If your macroalgaes have stopped growing, it's probably because they are doing their job.


New member
Something has changed in the conditions that is promoting diatom growth. Either you have new nutrients entering with your water changes (silicates, as mentioned above), you have overdosed iron (if you were dosing) or the macroalgae are starving and cannot grow.. allowing more opportunistic microalgae to gain a foothold.

You might consider more aggressive harvesting of the macroalgae in the future. For now, I would try to figure out what has changed. Are the lights old? Is the DI resin exhausted? Are you dosing anything new? Is the bioload higher or lower because of a loss/addition of fish or other inhabitants?



New member
I have found that lighting that is high intensity can grow micros over Macros IF: nitrates are too high, and phosphates are too high.. and not necessarily together. Reduce the light, use lower wattage, and shorten the time lights are on.. maybe even a half hour will help

In my experience diatoms appear after a new tank set up since 1) nitrates are high, and 2) silicates seem to be higher (probably from poorly washed gravel)..

If your tank has been up for a while, and its diatoms, perhaps you could have your makeup water tested for silicate levels. If this is the problem, a water change might not help much.

All that being said : Introduce some inverts that eat diatoms.. (snails help here):

If you have another tank to hold the cheato for a time, it couldnt hurt to remove it so that some of the foods (sugars and amino acids) leaching from the cheato get rinsed off)

I cant see any harm in a freshwater rinse of cheato.. but doing so will remove any copepods and other critters you may want to send to your display tank

Your caulerpa wont take a rinse.. Mine even die off if my salinity drops because my makeup drip rate is too fast for my small, shallow tank.

Try some of these remedies.. let us know what works best for you.
I really think it helps to spend the money on test kits .. It will give u before and after success, water quality parameters for your tank set up.. and will give u something to shoot for the next time you get a micro outbreak of some kind. :)

learning this sort of thing is satisfying for me.. makes the hobby a continuing source of interest.. even when I get frustrated as ( bleep!) :)


In Memoriam
By parts:

Silicates could be higher. I don't use RO water for ater changes and city water may have changed recently . I am getting a RO/DI unit today.

The tank is 1.5 years old, so I don't see that being th reason.

I will try some snails. I had a bunch once, but now only a few remain.

I may try putting the chaeto in a new tank. I have a few laying around. I would rather not freshwater rise it as it is crammed with mini brittle starts, you can see legs up all the time

Thanks for the replies!