1st grow - 3 Autos

Hi guys. This is my first grow. I am running 3 AUTO plants in 3 gallon fabric pots using jacks magic and perlight (70/30). The tent is 1.2 x 1.2 x 1.6 in a spare bedroom so the climate is stable. Carbon filter, fan, humidifier and heater all in the tent. The heater and humidifier are automatic and the environment is kept around 23 degrees and around 55% humidity. Passive air intake. The seeds I am growing are; Gorilla infested gelato by dr krippling. Mango blueberry bubble (free) by fast buds. Zkittlez auto by fastbuds. I was intending to start a diary from the off but I have struggled for time. Looks like I do need some help here so I have decided to put this together. Grow started fantastic running into no issues. The gorilla and zkittlez were the biggest plants. I introduced nutes in week 2 at 1/4 strength. I have been gently lsting all plants from the start. As you can see from the images I have ran into a few issues in the past week. This started when the lower canopy started to turn brown and die starting from the tips (bigger fan leaves) on all 3 plants but mostly the zkittlez. I gave them all a little water and introduced topmax and bio bloom at half strength as it seemed as if this was a deficiency. I then started to see small irregular areas of damage. Again I have tried to show this in the images. It was like there were some form of pests but after hours in the tent checking with a microscope I feel pretty confident there aren’t any. As a precaution I did make a very week fairy liquid solution and sprayed on the plants. This was washed off around 3 hours later. I read that this could have been caused by lack of airflow around the plants so I introduced a second fan into the room by my passive air intake set on a weak oscillating setting (this was on Wednesday the 31st). Since then it seems the plants have been recovering although the zkittlez may have suffered a little more as growth seemed to have slowed although she now seems to be coming back. The main issue now is this almost black, deformed growth I have on the gorilla infested gelato plants. This is shown in the last photo. Could these be nute burn? I haven’t been heavy handed so I doubt this or could this be a nute deficiency or maybe my light is too close? Or it could be wind burn? I was thinking to flush the plants or just water with pure water and check the run off ph to see if they need flushing. What do you think? I am a bit lost as to where to go next with these girls so would appreciate any advice. Sorry if that was a long read and I hope I have been clear. This is my first grow so these issues were bound to arise.