Diatoms in well established Reef

[Scubabum]

Over the last two weeks I've noticed what I think are Diatoms in my 20+ year reef tank. In the attatched photo, it appears redish but in person it's more of a brown shade. I'm using RO/DI water at 0 tds and my parameters are PH 8.2 Alk 9.1 Ca 420 Mag 1320 Nitrate 4ppm and Phos .05 ( a tad higher than usual) Lighting is a Kessil Ap700. The only thing that has changed in my tank recently is I added two golf ball sized, uncured Pukani Rubble rocks from BRS, that I mounted a couple of frags on. Do you think the diatoms are coming from the Pukani or does anyone have any other ideas or thoughts? Could it be Cyano? Thanks in advance.

free upload image

 

[nex64]

You have a silicate test? That could potentially be an issue

 

[Scubabum]

You have a silicate test? That could potentially be an issue

Thanks for the quick response. Unfortunately I don't have a silicate test. Doesn't the DI resin remove silicate? My TDS coming out of the DI resin is Zero.

 

[twilliard]

It is common to have diatoms in a tank no matter the age.
The best way to understand this is in the general biology here
https://en.wikipedia.org/wiki/Diatom

 

[nex64]

Silicates could also be potentially leaching from the newly added live rock. Only way to eliminate such a theory though would to test of course :)