Hi, I have the TF-100 test kit. Regarding the R-0013 that comes with it, I ran out of this. I find other sources for this chemical reagent (Taylor brand) , but they all have various alpha characters after the number, for example, R-0013-E, R-0013-F, R-0013-A, etc. But, I have a feeling this is just to do with the size of the bottle. Does anyone know?