Looks like a nute problem coupled with ph, most likely nitrogen. Flush, re-ph and use 3/4 to full strength veg base nutes. Use micronutrients to make sure its nothing like molybendium or iron deficient.
So if yo not checking ph then yo most likely not testing for ppms either right? Yo need to reconsider this method of growing and get some meters~ Or have yo even fed any nutes yet? Is there any nutes in pro mix 4 I've use sunshine mix 4 it didn't have nutes and yo have to give'em some and the right amount at the right ph~