Help! Algae ID

Already running GFO. Have replaced it every 2 weeks with this algae issue. DI resin is only a few months old and would have had about 300L max through it. Oh, and I'm running 2 DI resin stages in series on my RODI filter just to be sure.
Should I be doing anything more for silicate control?

 

I have what I think is this in my tank. We looked at it under a microscope and were unable to identify it. Our guess was a sponge of some type. It is photosynthetic
Silica is almost definitely my issue. I am on well and co2 was depleting my resin in less than 50 gallons. That has been fixed.
Limiting silica input and exporting it should fix it.
Silica has a very weak bond to the DI resin, when it gets close to being exhausted it will be replaced by something with a stronger bond and get into your water. This is almost always the source. You might be able to get a silica test to test your rodi water
You aren't on well water are you?
My only suggestions are changing the resin and changing the gfo more often. I don't know much about the bond between gfo and silica but it might also become exhausted within a few days if silica levels are high. I imagine testing for silica in the tank would be like testing for phosphates, with this stuff consuming it there might be little if any free silica in the water.
My strategy is replace the gfo weekly and use a turkey baster to blow it off the rocks. It has only been a week since I have dealt with the co2 issue in my tap water but I think I already see a decrease in this stuff.

 

I might add that diatoms are another silica limited organism. At the end of their life cycle they fall to the bottom of the tank, so if you are BB, be sure to vacuum out as much detritus as a method to export silica.

 

OK I will get a silicate test kit when I can find one (marine aquarium supplies are rare here in New Zealand).
My RODI water reads at 0ppm, but yes I am on well water...

 

wells are notorious for co2, and that will exhaust your resin in 50 gallons. Might be better to invest in a co2 test for your water.
Here is a link to spectrapure and a basic design for a degassing tower to remove co2
Technical Service Bulletin, February 1996, TSB No.103 by SpectraPure, Inc.
http://www.spectrapure.com/CO2_SYSTEM.pdf

 

In saying that I am on well water, I think it's pretty good for a well. TDS out of the well is ~80ppm. In fact, the Christchurch city tap water is sourced from the same aquifers as our well water.
If my DI resin was exhausted, due to CO2 or otherwise, wouldn't I see a rise in TDS in my RODI output? It is still a consistent 0ppm.

 

I guess it would depend on accuracy of the the TDS meter, whether its calibrated correctly and of good quality. I am just going by my experience with well water and that I have what looks like the same thing in my system.

 

So another update.

My partner had surgery so I haven't done most of the things I intended to do, but...

It's been 4 weeks since I finished the blackout. I had the lights at 3 hours (+2hrs for actinics) for 2 weeks, 4 hours for 1 weeks (+2 hours) and the last few days have been 5 hours (+2).

So far the algae has not returned ;D

My corals have better PE than ever have noticeably grown in the last few weeks.

I have had a few other algae species creep in (hair algae and some halimeda), likely due to nutrients released during the original algae dye-out, but nothing unmanageable. I've upped my carbon dosing and turned up the skimmer to help with this.

Fingers crossed that this is the end of this horrible crap!

 

I did 2 5% water changes, changed DI resin and changed the gfo weekly for 2 weeks. No sign of it in my tank.