Assuming peat is part of your homemade mix just add more peat to it.

Dave

I would mix it with an equal amount of the original pH 5.5 medium.

Actually, Dave beat me to it! :)

This post was edited by Slimy_Okra on Sun, Mar 16, 14 at 21:07

Thanks for the suggestions! My mix is partially peat based, but that actually leads to another mystery. I'm using a product called "Turbo Peat" from Canada, which as far as the label says is just straight peat (no fertilizer additives, etc.) But whenever I've tested its Ph, the readings come out about 6.5 ish, in other words, not very acid.

Obviously, I must have had something acid in the mix to make it acidic, and indeed the peat is the likely answer, but I just have this weird testing result.

I would double the size of the mix, but I just don't need that much seed starting mix. But thanks for the idea, I may well go down that route.

Are you sure that whatever you're using to test the pH is accurate?

What kind of pH tester are you using ? How reliable is it?

Anyway, I would reduce pH to 6 to 6.8. That is ideal.
As far as fertilizing, seeds DO NOT NEED fertilizer to germinate or even til they have a couple of true leaves. Then you can start fertilizing by 1/3 strength liquid fertilizer solution.