I have a 20g tall with substrate planted Wisteria and a floating mass of Anachris and Red Leafed Ludwiga . It all has been growing fast enough that Iv'e been cutting half of it out once every 3-4 weeks. Then I started keeping the water level about 1.5-2'' below the top. ( I had been keeping it .5'' below the top.) I did my usual cutting and although the Anachris and Ludwiga bounced back as usual, the Wisteria has really struggled. Could the lower water level reduce light?