Hair Algae on sand and rock

[FingersCrossed]

I have a 120 gallon tank that was doing great for 4-5 years with occasional algae outbreaks, but I was always able to get it under control until now. Hair algae has gradually taken over much of the rock and sand over the past 4-5 months. I'm regularly removing some of it manually, but it grows back quickly and has recently gotten worse, with growth over much of the sand and also between some of the coral. See pics. The rock in first picture is covered with green star polyp which has recently been overrun with algae.

Parameters -- Salinity 1.0235; Calcium 425; kH 9.2; Magnesium 1320; Phosphate and Nitrate - both measure at zero, presumably because the algae is consuming them.

The tank has following 8 fish: 2 clown fish; hippo tang; foxface; sailfin tang; sixline wrasse; longnose hawkfish, and a randall's goby. I typically feed 1 or 2 cubes of frozen mysis or brine shrimp.

I have a pincushion urchin that has done a great job clearing the algae off the back wall of tank but maybe because it's busy with that, it doesn't do much on the rock. And I've got ~8 hermit crabs, a conch, and a bunch of snails (~20 now, a bunch have died). I'm hoping to get some turbo snails but the LFS hasn't had in stock for quite a while.

I've been using Chemipure Elite and some additional GFO (1/2 cup). I put these in high flow area of sump - I don't have a reactor.

I want to get more aggressive about getting rid of the algae. What should I do?

* I will plan to more regularly manually remove
* Do I have too many fish? (I would think these 8 are fine in 120 gallon)
* I currently just drop the food cubes into the tank, should I be defrosting/rinsing to remove potential phosphates? (I just read that, but wondering if it's worth the effort)
* What should I do about the sand? Should I replace some or all of it?
* Should I consider getting a reactor for GFO / carbon?

I know there isn't a magic solution, but appreciate advise on what may help the most.

Thanks.

 

[Saltyreef]

Manual removal, increased water changes. Cut back on feeding a bit. Are you using RODI? If so are you maintaining that system properly?

 

[FingersCrossed]

Thanks. I have RO system. The output is reading at 2 TDS.

 

[Saltyreef]

Thanks. I have RO system. The output is reading at 2 TDS.

is that the RO output? Or do you have DI cartridges and thats the final product TDS?

 

[FingersCrossed]

I don't have DI cartridge -- the final product water is TDS =2.

 

[Saltyreef]

I don't have DI cartridge -- the final product water is TDS =2.

You might want to consider using them to polish your RO water down to 0tds.
Theres many things that can make it through an RO membrane and in turn, cause these types of issues.
The city wont send you a notice when they decide to alter their biocide program or switch water sources.