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u should just get a proper remineralizer like the GH/KH+. But failing that, remineralize RO water to GH 6 (TDS 120) and then add baking soda (potassium bicarbonate preferred) until KH at least 3. Then the TDS will be whatever, but remember this number for next time. It is pointless to test the pH of pure RO water because there is no buffering effect / the ionic strength is too low, so the tests are meaningless. With a KH of 3, the pH will not swing very much. (I think the pH swings are due to lighting causing plants to suck CO2 out of the water. The pH will be lower with lights off) Anyway, I blame the problem on whatever is causing the surface film. The water is obviously polluted.

You are doing something wrong because pure RO water has no buffering capability, i.e. no ability to hold a pH value against adding other chemicals. If you remineralize with GH only, usually those chemicals will put the pH in the low 6's. Even then, the ionic strength is weak, which means that most pH tests are invalid anyways. if you add small amounts of bicarb, which is a buffer, then the pH should rise. With that being said, KH for CRS should be lower than 2 max. There is another thread on this site from Steen and his 17 gallon tank where he also fights this bacterial disease. There is a whole lot of drama, but in the end, I think what worked was H2O2 (nuke the bacteria), water change (remove the bacteria) and Dr Tim's All-in-One (add back new bacteria). I am not sure how the last step helped, but ok whatever. Be careful not to overdose with the oregano oil and go in little steps at a time.

Ok cool. I can add an Indian almond leave. So oebt would do great? And yes I have my painted fires in this tank

Ok I'll try and test at the same time and see what I find! As for the shrimp, all had died by the time I got that 7.6 ph reading last week. I had 1 shrimplet survive until yesterday when I found it dead.