Help please nutrient issues?

Hello, I have been growing 3 plants in a 4x4x7 grow tent and I'm running into what appears to be some sort of nutrient burn/deficiency and I'm unsure how to treat it because I'm not sure if it's nutrient burn or potassium deficiency or what. This is my first grow ever so I have absolutely no experience but I do have pretty good knowledge on the subject. I'm just looking for some help diagnosing what's going wrong with my girls. some background information they are at day 25 of flowering I'm using a 400 watt hps light as well as a vent fan and an oscillating fan. I also spray some cO2 in there every few hours not sure if it's helping but i do. Also the soil is white because the top few inches is play sand to keep fungus gnats under control. Another sidenote I started them under cfls for the first 4 weeks and due to not understanding my light timer they got a 23/1 light schedule rather than 18/6 as I intended. For nute's I'm simply following the directions of a starter kit and there's been no big change in nutes other than a slight increase in volume of watering ,not concentration of the solution. Please help this is my first major problem I don't know how to handle.

just an update I usually water every other day with a gallon of nutrient solution with biothrive bloom 10 ml, cal mg 5 ml, biothrive bud 2.5 ml, biothrive marine 8 ml, and 5ml of fishshit(literally the name sorry). I'm thinking it's either nutrient lockout or a potassium or magnesium deficiency. I'm thinking of switching to a water feed water feed schedule and seeing if that helps, but any advice would be appreciated.

Your second pic looks like PM...otherwise, your plants look pretty good. I'd give them all a once over and be sure PM is not your issue.

Good luck friend.

Yea I had my water tested a year ago but things change might not be a bad idea to check it out, I had wondered about that myself but I lack experience. thanks for the input appreciate it

Usually a lockout occurs due to a buildup in salt based fertilizer
Most manufacturers recommend to high of feed schedule ( to sell more product) and thus the build up, cut back to half measure and the alternating water/feed schedule and see how she goes