I agreed with fshfanatic. regular dose excel works well to kill BBA. Seems like you have bba attacking your crypts which is pretty much the same case as mine. what i did was collect 5ml of excel into a syringe, turned my filter off and spot treated the affected leaves... leave the filter off for 30 mins and turn on... I have used it on mosses as well, it works but i slightly melts down a bit of the moss.. but i does recover... using this treatment is more effective than overdosing the whole tank. I learned this the hard way as i lost quite a bit of amanos using the overdose tank treatment... (which works too btw) but i find that spot treatment is more effective and less detrimental to shrimps if you have any in the tank.
you should see the bba turn red and die off...
what i suggest is get a drop checker too to make sure you have a monitor on the consistency of CO2 saturation in your tank
