Aquariums: HELP! Seeking advice on persistent algae

I already tried asking for help 2 months ago for this problem on Reddit, without any response.

The problem is a bit more serious, but hasn’t changed much since then.

Here is my original post:

Hello,

I’m reaching out regarding a recurring issue that I’m bringing up again as it might be specific to my tank’s parameters.

It’s a 60L tank set up three months ago, densely planted, with technical substrate, JBL CRISTALPROFI e702 filter, Chihiros Serie A lighting, and CO2 injection (adjusted according to the drop checker reading in the aquarium). The water temperature is set at 25°C.

The tank is home to a dozen Danio margaritatus, around ten Caridina Logemanni shrimp, and three Amano shrimp. I only feed the fish once a day in very small quantities; everything is eaten, and any leftovers provide food for the shrimp, which currently aren’t specifically fed.

Here are the water parameters (measured with drop tests and confirmed with test strips):

* pH: ~6.5
* NO3: ~10 ppm
* NO2: ~0.3 ppm
* KH: ~7°

For the past month, I’ve been dealing with green filamentous algae, and some brown algae have also started to appear. The problem is worsening despite my efforts to control it.

I perform water changes (1/3) twice a week with slightly remineralized RO water, and I try to remove as much algae as possible every two days, but they keep coming back in larger quantities. For now, I’m not adding any plant nutrients to the water, fearing it might exacerbate the algae problem.

The lighting is set to 8 hours per day at 50%, and I’ve already tried reducing it to 5 hours per day for a week, with no success.

I believe my nitrate levels are too high, but I can’t seem to bring them down.

Should I attempt a full blackout? Is there a risk for the inhabitants to be in the dark for several days? What can I do to reduce nitrates?

Do you have any other recommendations? Thank you very much for your help!