Green hair algae help pls?

32 g bio cube after many months of battling this green hair algae problem I am officially asking for help. Recent pics attached. I think I have tried all but chemicals and today after many many tests of zero phosphates I see a 4ppm (yes 4ppm not 0.40ppm) phosphate reading. I also just lost my lawnmower blenny Saturday night I noticed he was dinner to my cuc (but he only mowed in his dreams, he mostly picked at the glass) and also lost one of my urchins Thursday (had 4 going). Have manually been vacuuming the long hair algae to a paint strainer (new of course) and pumping that clean water then back through filter floss in my sump. Awful process btw and clowns are now biting me as I guess they are sick of me messing with their house. Have tried lights off for a couple days. Cooepods. Lots of cuc. Manual vacuum. Water changes. I have always used the rodi from Petco (it’s time for my own, yes). What the heck else to do soon can get this tank to the fun part and maybe finally get to that big tank really want. Glass is clean. Sand is clean. Back wall is spot less except for bottom return flow. I turned the flow pump off 8in holes to stop spreading more algae as it seems like water clarity is worse when running the flow pump. Stock circulation pump.

Cuc-
3 urchins
1 maybe 2 Mexican turbo snails
~2 dozen various snails and hermits.
Copepods dosed a few bottles

Current stock
2 clowns
Royal gramma
Six-line
Cleaner shrimp
Watchman Goby (unknown if alive) - spotted 2 weeks ago in my pump chamber (he’s an inch) and added back to display and now vanished again

Previous stock (Rip) not all together
Lawnmower blenny
Flame angel
Midas Blenny
4th urchin
Multiple large turbo snails (mind boggles me with all the algae).

Nitrates zero
Nitrites zero
Ammonia trace 0.25ppm to zero
Ph - 8.2
Phosphates 4.0ppm (zero for months)

32 bio cube
Tank started in February
Skimmer
UV sterilizer
In tank media with floss on top chemo pure, carbon bag, bio rocks.

This is one of four AIO nano tanks we run. Been at this hobby for some time but still feel like a total beginner and do not have much of this figured out. I do enjoy the constant challenges but time is limited and get really stuck with conflicting information (or that I don’t understand) when researching! This one I hate that I cannot beat the algae, not giving up but admitting I need advice, please help and thanks for your guidance in advance as I know a lot of great knowledge on this site.

Grab a sea hare. It'll make quick work of it and they are the coolest

Before using chemicals you need to figure out the cause. What and how much are you feeding? Did you test the Petco water yourself to see what the levels are?

This looks like turf algae, not a regular gha, which is tougher. I agree with MadReefer, identifying the source is important. Zero nitrate and very high phosphate is also suspicious especially since you’re doing water changes. Brightwell razor might work well for you.

Where in north nj are you?

I'd go with manual removal, turn the lights off for a couple of weeks since you have no corals and then slowly ramp them up again. You can always regrow coralline and it is much more resilient than people give it credit for.

Thanks all for the tips. Absolutely Fish has a few sea hare’s so I think that will be my next step and then if no go will have to try the lights out for a few weeks, I’ve only done a couple days at a time, and then maybe onto chemicals after that if need be but trying not to. I feed pellets outside of a little nori from time to time and never got to frozens. Maybe I didn’t clean the rock enough? Prob over-feed but like I said, not my first tank and never had algae this bad for anywhere near this long so something else contributing.

Water is the Petco imagination 5 gallon pacific water, not sure if you mean I should be testing that for phosphates or other water parameters before adding?

Looks like your rock was loaded with organics. Was this dry rock previously used in an old tank? With phosphate of 4ppm I would start dripping lanthanum into a 5 micron sock. An iv bag from Amazon and a few ml of tropic Marin’s lanthanum product (or another product) would be good. Lanthanum is only unsafe when dosed without the presence of po4, in which case it would precipitate into the water column and harm fish and lanthanum levels would build.

What type of lighting,age and photo period type of rock and substrate?

Yeah I was also wondering where your rock came from. Is the sand also fine sand? I once took over a tank that had rock with built up organics. I started doing waterchanges with my own water weekly, and it was like 50 percent waterchanges. I knew what I was doing so I wasn’t worried about killing anything. I added a powerhead to blow into the rocks, to flush out the builtup organics. When everything starts working as it should you should have any ammonia.

Honestly with that sort of infestation, I would either recycle the rocks or replace them. The rocks could be leeching the phosphates, so no matter what you do it will come back. Its a small tank and would be pretty easy to replace, we had to do it on a 205 and it was a process to say the least.