The "sludge" is a mix of water and whatever you have put on the bottom of the tank. Acidic mixes will inhibit algae. For me it is a mix of peat, dead u. gibba matter and algae [img]http://www.**********.com/iB_html/non-cgi/emoticons/new/smile_n_32.gif[/img] (moss will tend to float when you raise the water level so is not ideal). Trust me. You can see mine flowering above in the peat and water substrate. Just keep it well shaded and in plenty of water until you have a dense mat, and this will then outcompete algae when you bring it into summer sun. Raise the water again at the end of the summer and keep shaded for the winter.Originally Posted by [b
I grow other aquatics too and gibba is really not an aquatic in the same way. Things like vulgaris and radiata flower in deep-ish water (a good few inches at least), completely the opposite to gibba.
An examination of the flower stalks backs this up. If the plant was floating the flower stems would sink under water if visited by insects (imagine a floating version of sandersonii). Ripples in the water would also be likely to submerge the flowers. True aquatic flowering plants like inflata and radiata have even evolved to address this issue by adding floatation devices to their flower stems. With a firmer, sludgy substrate the tiny hair-like flower stems of gibba have support and stay upright:
When I first started with gibba I just floated it in water and it grew well but not much else happened. I would never now return to floating it in aquaria or tanks. I find little interest in a mat of green leaves unless it deigns to flower.
Here's a photo of it flowering in the wild, in what looks to be only a cm or two or clear water before the subatrate starts:
And another wild photo where there is no free water: