I saw your questions in my 1000L topic, but must say your tank doesn't look bad either! 2 thing which I noticed, the gravel is quite coarse which results in a lot of dirt accumulating in there and inducing algae. A second thing I noticed is that your old leaves all have holes in them which usually indicates low PO4 or NO3. Could be low CO2 (too much light) too. Do you know your water values?