I'm not positive that pH is the reason why your agar doesn't gel. In the lab at work I frequently mix up batches of it with plain tap water (pH 7-8) that I pour in petri dishes to keep leaf disks fresh for caterpillars. I use 7g/L which makes a solid agar, but it's still on the soft side and there's a thin film of water on it. I use 8g/L sometimes, and that's already much harder. I would think that you would need no more than 10g/L to get a nice solid agar. I don't even autoclave it, I just bring it to a boil in the microwave, shake the bottle and pour. Still gels nicely. I use electrophoresis grade agar from Sigma-Aldrich.
What else are you adding to your media? Perhaps something is contributing to the softless?
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Camille
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