Yellowing lower leaves

Hey guys, so today I was curious to see if anyone would be able to help me with a problem I’m having. I am growing six plants in a 4 x 4 tent with a viper spectra 600 W at 30 inches with white and blue lights on. Humidity is anywhere from 55 to 70% with room temperatures being anywhere from 68 to 80°. Last night my temp dropped to 67° and this morning when I woke up I noticed yellowing on one of my six plants on the lower leaves. All of the other plants are looking fine except maybe they need watered. I watered yesterday with liquid seaweed “1 mL“ and pH to 6.7 but I don’t think I watered enough because their droopy again this morningsnd feeling very light. Could I water again or wait till tomorrow? Anyone have any ideas what it could be?
 

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