starch is a fluid loss control agent at 4-6 ppb but not good or hi-temp and will bio-degrade. CMC or more refined PAC will also decrease fluid loss which comes in regular which will also incr. the vis or low vis. PAC conc. is 0.5 -1.5 ppb. Cypan (sod.polyacrylate) is very temp stabile at 1-2 ppb, over treatment will thin drilling fluid.