Hello again.

My 30ltr tank is running since October, all was good with no major drama until about 5-6 weeks ago when algae took over. My wife liked to feed the fish and let the lights run for ~ 10h a day, the algae mended her ways.

Drastic action caused the algae to disappear but the water remained cloudy so for the last 2-3 weeks I change ~ 30% water (10ltr). However, there is white foam floating on top with lots of brown algae (yesterday changed 13ltr and cleaned the plant's leaves with paper but today it looks as I did nothing). The water parameters are good, 0 ammonia, 0 - 0.25 nitrite, nitrate was not tested but the tap water are at 40ppm. I can't see the nitrite climb drastically in 2-3 days period.

Any idea what else can be done?

Thanks.

...and another photo (sorry, didn't manage to add in one post).

That looks like brown algae / diatoms. You might find this helpful:
https://www.thesprucepets.com/aquarium-algae-1379979

The white foam is most likely an accumulation of bubbles. Ensuring the filter outlet is skimming the water surface ought to address that.

Thank you.