My girls are dying, having multiple problems with plants

Hello everybody, this is my first grow and before i planted my seeds, i read lots of stuff about growing cannabis and i was thinking i was going to grow some beautiful plants with all those information i have learned. But in practice everything has gone wrong with 2 of my girls out of 3.

Some brief info about the plants :
Autoflower strains in 3-gallon soil under 300 watt COB full spectrum. It's in a growing tent between 25-28 celcius of temperature and 50-60 percent of hummidity. I am watering them once in 3 days with half a litre of water and i feed them every other watering with GH flora series(half dose of what is recomended. Always used ph'ed(6.6) water. They are 1 month in flowering. They have another sister which is healthy and showing no signs of def.

One of the girls had yellow leaves starting of the bottom and went upwards. At first i thought it is normal since it's in the flowering stage and getting the N from the leaves. I was not into giving more nutes due to the possibilty to burn the plant. But eventually she lost most of its leaves and still has yellowing leaves issue. With last feeding(yesterday) i added cal-mag(4-0-0) for the first time and raised the N a little bit(I normally add 0.5ml/L, i raised it to 0.70). But today they have purple spots on some of the leaves(Which i think phosphorus def) and twisted leaves near to the top. I'm really worrying if they are dying.
should i flush them or increase the amount of nutes ? Thanks in advance guys..

3 gallons of soil needs 1 3/4 gallon of water added each time the container is light and dry again.
stop the cal mag
you're feeding half strength when your ppm's should be peaked,
feeding half of what a plant can use, deficiencies are expected?
when I used GH I used it per bottle directions and was impressed with the results.
not sure if those are (the) problems but the first 3 I saw.

But they have burnt leaf tips. That happened after i raised the N and add cal-mag. Should i raise it to the full dose anyways ?

Yeah those things are choking. You didn't say what kinda soil so I assume regular garden soil, thats no prob.
6.6 should be fine for ph going in but what about ph coming out. I had a ph problem once, the water going in was 6.5 and coming out it was like 8! But I'd definitely say flush a lot of fresh ph'd water through it. Until ph coming out is normal. Then get started back on the note schedule but only feed them every other watering. between feedings should be fresh ph'd water

maybe check ppm of your run off for giggles before you murder your soil bene's?
I've never had a sick flowering plant recover to my satisfaction. When one gets ill half way through fowering here
I just kill it and take me lumps.

I think it is ok with ph because other plant has no issues and keep growing. These 2 are stuned for a while.

Shruum said:

I think it is ok with ph because other plant has no issues and keep growing. These 2 are stuned for a while.

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You shouldn't "think" anything.
Check it and KNOW.
Ive had plants from the same strains that responded differently to amounts of nutes and PH. I'm pretty sure you have an issue involving ph. Even if you didn't the answer for this problem would still be flush thoroughly with fresh ph'd water until the run off was almost exactly the same PH and PPM/EC as whats going in.

First off fill your pots right. That should have been he first thing you read. Notice how everyhing down deep in that pot is fucked? Theres less air flow. It becomes a humid, or arrid nightmare every other day for your plant. Your plant is starving. Like we should be donating .40 cents a day to feed starving cannabis plants hungry. You are on track for sure, just tighten a few things up. I agree wih nugs, if your ship is sinking, dont assume its fine because its mostly above water. Go and check it out. Even if cut from the same mother no two plants grow identical. G.I Joe reall sums it up the best. Knowing is half the battle!

It was full when i first fill the pot but after several waterings it went down. Is there any point adding more soil after this stage ? And after the flush should i feed with full strenght with the next watering ?

No dont add dirt now. Tamp your pots down a little,or fill them when the soil is moist to prevent that much drop. And id go somewhere between what you currently give them and full strength.