First Grow - 4 different strains

Big changes happening this week with a lot of growth. Having to individually monitor, diagnose and treat each strain under one light is getting harder and more time consuming each day but I am learning loads so im taking it in my stride. Each plant is taking up the water and nutrients at their own pace(obviously), so i'll have to water/feed when they do/don't need it, so much for my schedule feeding all 4 at the same time. The White Widow started looking droopy around the 3rd day of the week after feeding nutrients, when it stayed droopy I decided to skip the next water feed, the last day of the week it started looking better so I think it was just overwatering. The Amnesia Haze and Critical Churchill both have yellowing leaves, new and old growth. It does't look too bad but I don't want to let it get out of control so after doing some research I have decided to to test the runoff and do a flush with ph 6.5 water to get it back to a healthy medium. I got myself a real PH pen and TDS meter, so no more ballpark figures when feeding and watering. The Purple Merkel is growing big, she is still in early flowering and showing beautiful purple hues. The cold is getting pretty bad so I got some crates to lift the plants off the ground, I keep a small oil heater with a thermostat on during the really cold nights to ensure the temp doesn't drop below 20'C.