Diatoms and some algae.. Why??

J Rog · Oct 27, 2014

So over the past week or 2 I have been getting Diatoms on my sand bed and some algae growth on my rocks (not a ton).. But more concerned with the diatoms.. Tested last night and my Nitrates were undetectable with my Salafert test kit and PO4 was at .06 on my hanna tester.. I didn't think .06 PO4 was enough to start doing this. I have had PO4 higher with out this happening.. Any advice? I was running GFO and carbon but turned it off because i saw my zoas closing up and thought they didnt like the carbon.. But i think they were closing up because they had some algae growing on them.. As far as flow im running 2 vortech mp 40's at 100%. So flow should not be the issue either.. Tank is a 120 gallon 4 feet long

Chpaige · Oct 27, 2014

Light schedule, how long has the tank been up and running, have you changed food, water, lights?

J Rog · Oct 27, 2014

Light schedule has been the same for a while. Tank has been up since 2010 or 2011.. But come to think of it I did notice everything start happening after I changed out all the filters in my RO/DI unit. I changed the RO membrane as well.. Will a new membrane do that? I did run it for 2 hours (per the directions) to flush it.. I probably have done 3 water changes plus top off water with the new filters..

DFW · Oct 27, 2014

Silicates can be behind diatoms. Have you checked tds since you changed the membrane? Hopefully you did not get a lemon!

J Rog · Oct 27, 2014

Ya, tds is at 0. When I changed everything it was only at .01

Randy Holmes-Farley · Oct 27, 2014

Phosphate isn't typically limiting to algae growth until the levels are below your current levels, so lowering it likely will help.

Diatoms do need silicate, and if you are not dosing it (I do) and are not adding it in top off water, then the supply available usually runs out on its own. So the diatoms may be self limiting.

J Rog · Oct 27, 2014

Randy Holmes-Farley said:
Phosphate isn't typically limiting to algae growth until the levels are below your current levels, so lowering it likely will help.

Diatoms do need silicate, and if you are not dosing it (I do) and are not adding it in top off water, then the supply available usually runs out on its own. So the diatoms may be self limiting.

Thanks for chiming in Randy! So it should eventually go away on it's own is what your saying as long as everything is in check? Also, what's the reasoning for dosing silicate?

Randy Holmes-Farley · Oct 28, 2014

Yes, diatoms usually go away on their own if there is no ongoing source of silicate. That is likely why diatoms are often a time limited part of new tank algae cycles.

I dose silicate primarily for sponges, but also to encourage some diatoms so that snails and such can eat them and get enough silica.