Powder.

Further one can ask, if you are using with or without HEPES?. Nevertheless, I also need a basic clarification, which you should have mentioned in your question, whether you are talking of primary adaptation or continuous passaging?. pH definetly makes difference and so does the bovine serum (fetal bovine or bovine) also which source.  In primary adaptation we  have seen that every thing remaining constant, the drug resistant isolates are comparatively fatter. So you need to analyse your observation considering all the above confounders. Hope it helps you.

My apologies, these things were implied. Parasites from continuous passage show a fatter morphology when cultured in M199 containing HEPES prepared from powder rather than company-bought solution. I was wondering how adjusting the HEPES' pH prior to its inclusion in M199 might alter the osmolarity of the medium compared to a media that had its pH adjusted after the addition of HEPES.

i.e. HEPES>pH adjust>add to M199

or   HEPES>add to M199> pH adjust