If you don't have a pH meter, then why are doing this? That doesn't make a lot of sense to me! Anyhow, if you are in peat / compost, then just water n' go, don't be using vinegar to adjust your pH level when you don't even know what that level is! Other than that... it could be cyclamen mites, or broad mites, but if its not them, then it is a pH imbalance probably brought on by all that vinegar you been adding to your water.