What is this?

[persvensson]

I Have this 15g macro algae tank, and it’s been up for about 6-7 months, what could this be? What would I do, I make 20% water change every week.

 

[Skywater]

The film: looks like a slime algae/ cyanobacteria. Grows in low nitrate and only needs a little phosphate to grow. You may need to add a little nitrate to balance the phosphate/nitrate ratio. I have lots of macroalgae and dose potassium nitrate. (DYI recipe from Randy Holmes forum)
Increase water flow if needed. Make sure all parameters are optimum.

 

[Subsea]

I Have this 15g macro algae tank, and it’s been up for about 6-7 months, what could this be? What would I do, I make 20% water change every week.

Fast growing Caulerpa will strip nutrients from the water. The big three nutrients (N, P, K) are not in your salt mix. Nuisance algae like Cynobacteria & Dinoflagellets thrive when nutrients bottom out.
I dose my macro tanks with ammonia & liquid kelp concentrate. Many use ChaetoGrow & iron.

What is your nitrate & phosphate in this tank. The ratio of N:P is not important. It is only necessary to have some: P>.03ppm & NO3 > 5ppm

 

[persvensson]

Fast growing Caulerpa will strip nutrients from the water. The big three nutrients (N, P, K) are not in your salt mix. Nuisance algae like Cynobacteria & Dinoflagellets thrive when nutrients bottom out.
I dose my macro tanks with ammonia & liquid kelp concentrate. Many use ChaetoGrow & iron.

What is your nitrate & phosphate in this tank. The ratio of N:P is not important. It is only necessary to have some: P>.03ppm & NO3 > 5ppm

Im pretty positive that my nitrates are 0 should I gradually remove the macro from the tank and just leave a bit in? Not a fan of dosing chemicals to tanks.

 

[Subsea]

Im pretty positive that my nitrates are 0 should I gradually remove the macro from the tank and just leave a bit in? Not a fan of dosing chemicals to tanks.

Nutrients/chemicals are building blocks of everything that grows.

Perhapes you should feed the tank and allow fish poop to feed the biomass.

No need to be gradual about removing macro algae.

With respect to what looks like Cynobacteria, vacume it out with a partial water change. However, until you get some nitrogen in the water the Caulerpa will struggle and the Cynobacteria will outcompete it. It looks like some cyno is growing on the Caulerpa as well as the substrate.