Troubleshooting my mix

[clkingtx]

I started my seeds in February/March this year, mixing potting mix from old pots(houseplants that died), and dirt I dug up from my yard.(It was all I could get at the time. Other than a few problems with damping off(but not as much as I expected), I got nice starts to go out in the garden. When I was able, I bought peat and perlite, and mixed the two for my seed starting mixture. I don't think my babies and seeds are doing as well in this as they should. A few seem stunted, not growing as well as they should. I put a jobes fert stick in each, but they don't seem to be doing too great. I thought maybe it was just one of those things, but I just saw that a tomato seedling has purple leaf bottoms(cotyledon leaves). I know it is not the cold, as they are outside, and temps have been warm enough, plus none of the other tomato seedlings are having that issue. I had read that sometimes peat is too acidic...I had used peat/perlite/vermiculite(1/1/1) in the past, and it worked perfect for everything. I just didn't have the funds this time around. Could my mix be too acidic? Is there something I could add to the mix as is, or would I have to combine with vermiculite to neutralize ph? I have potted MANY plants with this mix, and it only seems to be the tomato seedlings that are having problems, that I can tell. All the others plants(older tomato, pepper, citrus trees, lambsquarter, etc) seem to be doing fine.

Thanks a lot,
Carrie