I have a thin opaque scum that builds up about 24hrs after a water change that i can't seem to get rid of. I have tried adjusting the output from my external canister filter to be just under the surface and have good circulation and an air stone at night but it keeps returning. Co2 is good as confirmed by calibrated drop checker method, 55w AHS lighting over 16G tank & EI ferts. Glosso expanding, tonina, rotala occultifolia, blyxa, hair grass are all growing well. How do i get rid of it and stop it from returning

You mention using a canister filter.. you can purchase surface skimming attachments from Eheim, Fluval, etc.. that effectively remove surface film in freshwater tanks. I have used the Eheim version and it was very effective providing the water level doesn't fluctuate more than 1/2 inch.

RAS

P.S. Attached is a pic

I was hoping for a solution that didn't include putting more equipment in the tank.

Ive used one of these before, all they are is a tube for the inflow of the filter, with a gauze bottom, and a gauze top.. most are adjustable so you can set it to take more or less inflow from the bottom and the top.

Theyre very very cheap and work really well.

SS,

I've done larger water changes and cleaned up the tank as best as I can.
I also noted a correlation between sub optimal CO2 levels and pearling and SS layers.

Tanks with issues, sometimes for months where cleaned up fast when I added more plant biomass, increased the CO2 a little and optimalized things.

When plants are stressed due to CO2, they will release lipids and proteins that are hydrophobic. That's the scum. Foamy scum: lips/pro's+ fungi.

When plants really do well, less and the fungi being aerobic are easily able to handle the waste.

Regards,
Tom Barr