This could be last week's news. As long as the most recent growth on the top leaves look good, it means that you did have a problem a few days ago and that it was cleared up quickly. If you look underneath the damaged leaves and find anything looking like a bug, then definitely get a stronger viewing accessory and try to identify the pests. This could be something easily cleared up by a single spray-down with some Neem oil. Google hydroponic supplies with your zip code for local sources; online sellers are cool, too. If all else fails, go to a local garden center & ask for help with your tomatoes.