Algae ID Please

[fraglerock]

My 75gal reef tank is 12 months. It has developed a rust color algae all over sand bed and LR.
I use a RO/DI filter. I did a water change with tap water and conditioner when my RO/DI filter was down soon after the rust color algae developed.
AN ID and solution would be greatly appreciated

 

[meowzer]

almost looks like diatoms

I can't imagine one w/c with tap would cause all that though
what is your cuc? What kind of flow do you have? test results? what do you use for filtration?
do another w/c with ro/di.......try to siphon some of it out when you do.....and plan on doing another shortly thereafter

 

[fraglerock]

Salinity:1.024
pH: 8.21
Nitrite:0
Nitrate:40
Calcium:430
Alkalinity:2.5
Phosphate:.5
27 gal Sump/Refugium
2-150watt MH, 2- Actinic T-5

 

[fraglerock]

It was treated for red slime. Didn't help with the rust algae.

 

[cranberry]

It's diatoms....