Decaying leaves are a source of ammonia, which when enough light is available, causes algae to"believe" they are in a good place to take off. Hence the reason we often see algae on old, broken or damaged leaves, those leaves themselves are the source of ammonia. When those leaves are damaged due to malnutrition and you don't fertilise, you accelerate the algae formation. Lucily light levels seem low. There are some nice vids on youtube for making a diy skimer out of a cooldrink bottle, some floss and a small pump. It will clear of the mess in a few minutes.
I agree lift the water level till you get to the lip of the filter, it will also cut down on the noise.
Cape Town, South Africa.
Hi. I'm back.