8" of leaves dead, fell off rust spots no curling. Yellow spots on top help please

I was aay from three days and the first 8" of growth died and rusted and withered, the tips are yellowing. The water level was low so I added two gallons of ph adjusted 6.3 h2 o with 1 Ml dyna bloom so hopefully that helps. Can anyone tell me? Also I have what appears to be bugs eating parts of it too but no webs or black specs. It's cold outside so I thought this was harder. I don't have access to any gro shops for another week so if anyone has any good ideas I'm willing to try anything.

Anyone that can help will ask for pictures first man. Go ahead and post a couple if you can

WTF??? Sounds like you are hydro?
If so, 6.3 is too high, you want closer to 5.8View attachment 2388821

sorry there wasn't a lot of info on here. it's one plant starting third week into flower in dwc, plenty of air in water, 75 deg temp, 60% humidity, 120 watt(actual) 2600k cfl. no signs of bud but has what appear to be female preflowers. for the last month been trying to control a problem with some of the lower leaves having a rust like quality on top of a few of the leaves that are on the bottom of the plant. when they curl and die , theyd be trimmed but thought it was a nute deficiency or burn so followed purpdaddys 8 step guide and put 6 gal worth of nutes, 1 tsp dyna bloom / gal, in 7 gal res and 10 ml ph down as well as one cap of 3% h2o2. normally water is topped off with ph adjusted 6.o water every day and nutes changed every 7 days but after reviewing logs, the res accidentally went two weeks without change. came back after three days to find 8" of bottom leaves to be dead or dying, brownish, curling, raised yellowish and what appears to be bite marks. The steams also fell off with a light touch. put 2 gal of ph adjusted 6.3, one gallon had 1 ml of dyna bloom, and things look better but not cured. now just edges of some leaves have browning, some are yellow, drying out and dying on the branch, or have yellow pale spots. also some of these are curling inward. the current conditions are same but water ph is 6.3. there have been many mistakes but this is the first time trying. really would like to be able to finish this baby out. any info or suggestions would be awesome so this can finish this out.
pics below but quality sucks because of camera. some leaves that had fallen off were just put against a background. thanks in advance everyone

Again, 6.3 is too high.
Fix that and see what happens and report back.

Did another change and lowered ph to 5.9 . Colors comin back but lower leaves are still falling off pretty easy. Light is penetrating clear to bottom

They will pick back up dont worry give abit more nitrogen to the girls and keep your ph stable, this will fix all your problems and be patient because it will talk a week or 2 before you see the full results of recovery, actually probabley sooner because your plants are in flower so they are uptaking nutrition much quicker.