I agree with Aris. It definitely looks like the pH is too *low* (too acidic). If it were too high, then you would have a smooth, non-crumbly cheese (less acidic cheese knits more easily and produces a pliable paste).
Cheddars are a bit tricky. Lots of ways to go wrong, but the place I'd start improving is when you are cheddaring, taste the whey every 15-20 minutes. You want to stop cheddaring when it starts to get noticeably tart. Then cut the curds, salt them with half the salt, let it mellow for 10 minutes or so, then add the rest of the salt and press.