I do 50% water changes every week as it is, but have to feed my discus frozen food, which as we know is high is phosphates.
The algae is a thin covering over the leaves, so it is not beard algae and yes I have eight saimensis in the tank at present who are busy trying to get rid of the problem.
As for the Ph problem I think that it was probably like that for over five months, thats when I really started to use too much CO2.
Have now put in polysperma of two varieties, Rotala wallichi and Macaranda in tank. I hope things should now settle down.