I had this overwatering my two current grows, and then got worse for the bottom leaves only into the next week. I fixed this watering around the outside only until runoff and pruned the yellowed leaves. Both plants recovered. The answers from our more experienced peers @GrowingGranny @DutchDoobie @m0use below definitely fit the same trend also. In addition to @m0use 's comment about providing oxygen to the roots, air pots are a great way to go for this and I have been told that they can increase your yield. So I think between us, you have a solid answer. Good luck with your grow.
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