Hi Martin,
just to let you know that I don't have any more diatom in my tank !!!!
I have add a lot of hygrophilia to up the biomass, and I turned off CO2, reduce my flow and reduce light.
After two weeks or more of this regime, no more diatoms, after I decided to turn back CO2 very low, and it seams to work fine, plants are pearling.
I have added two weeks ago some monte carlo and some staurogyne and they are doing very well, pearling and sprouting new big leaves !!!
I think that what have realy helped is the higher plant mass and maybe my filter and tank is finally mature !!!!
I am very happy I will add some other plants this week.
cheers mate !!!