Split your media into 2 and sterilize.

1.Sterilize 1.5g/L MgSO4.7H2O alone

2. All other media components except (1.5g/L MgSO4.7H2O ).

after sterilization you mix both, you can avoid precipitation.

Cheers! I don't know why I didn't think of that. I'll give it a go :-)

Dear Stewart, We use KB all of the time for our pseudomonads and there is a really easy way to avoid precipitation: we add the magnesium sulphate and phosphate to the water (~800 ml which will be made up finally to 1 L, or directly to 1 L if we are being a bit lazy) and stir that until it is dissolved. We then add the glycerol while it is still stirring, and then the protease peptone (we use No. 3 from BD). Once everything is dissolved we add the agar, give it a brief mix to make sure that no lump forms at the bottom, and then autoclave it. Sometimes we find precipitates form but I don't think this is really a problem either for plates or liquid media - we just mix the agar as well as we can before pouring it out. We tend to use RO water, and sometimes see precipitates forming when the filters are getting old; different supplier's agar can also be an issue. Regards, Andrew.

Thanks everyone! I tried having separate aliquots of MgSO4.7H20 and K2HPO4, autoclaving and adding them to the sterile molten agar... worked like a charm! No lumps for me.

Another option is to buy a branded version like  Difco Pseudomonas Agar F. More expensive, but saves a lot of labour. And in my 30 yrs experience, even if there is a precipitate it has no effect on the growth of Pseudomonads.