Diagnosing problems is seriously confusing

Hi there! First time poster here.

My issues started around the 4th week of flowering and have happened before (I think it was the same) in my previous grow. I have leaves that are starting with yellow veins, progressing to crusty, brittle, brown and burnt out. The last 2 pics are new plants in a separate half of the system, with a full starting dose of GHE nutes to test how they handle this straight out of rooting. What I am seeing there looks like burnt tips yes? However, my main issue is the brittle dying leaves. The worst of them are pretty advanced (7 weeks) and the bud is frosty and looking great once again, no complaints there, but I know this is not simply late flowering dead leaf syndrome and everything I read seems to contradict the last possible cause/solution. Here are some pics:



I have a relatively small grow indoors. It is somewhere between an NFT and ebb and flow hydro system. I say this because it top feeds through the pots and drains quite slowly without much of a slope. There is also a small amount of water that stays in the system between watering (no more than 5mm). The pots are about 7cm across and 10cm deep filled with hydroton and then suspended slightly above the bottom of the troughs. The troughs are covered with a heavy black plastic which just about cuts out all the light (I have no slime issues in the troughs). The water runs on variable timings, either (on/off) 15m/15m, 15/30, 30/30, but this used to be 15/15 before my problems started and I don't think it is a cause because the system could deal with constant flow seeing as the roots are in no medium for the most part. However, I try to give it a break and let it dry out a little.

The reservoirs are well oxygenated (I believe) as I have a couple air stones in them and use 5-10ml of 50% peroxide in 40 litres every couple of days. The reservoirs are 40 litres and pump up through black piping to the top of each pot.

I use GHE nutrients at around 50-75% of the recommended dosages (normal.. NOT Lucas formula that did not help and may have worsened my problem), which leaves me with a PPM of around 300-450. These are the ranges I have tried so far. I have a 0.5 factor TDS meter and this has always made me wonder when people talk about 1000+ PPM because I have definitely had some nute burn (if my issue is not exactly this) before. What confuses me is that people recommend half to 3/4 doses of GHE for marijuana, and they get ppms of over 1000. I do the same and get 300-450 and my meter seems vaguely correct as it reads rain water that has run off a roof as 25.

In 3 separate runs of the grow now, I have always had a fair amount of PH fluctuation, sometimes as much as 0.5-1 point in a day. The only time it seems to sit pretty at 5.5 is when I have managed to make a fresh reservoir with spring water that is already 5.5 and I haven't corrected it. It has dropped in flowering and risen in flowering, though not up AND down day to day. So this is also confusing as I try to keep my methods as similar as possible to eliminate problems.

I use either spring water (some of the best known to man at a ppm of around 50 on my meter) or rain water off my roof (has some visible particles in it and a ppm of about 25).

My temperatures and humidity are as follows (a little under the tops of the plants) - 80-85F and 40-50% in the light cycle, 65F and 70% at the peak of the night cycle (read off a min/max thermo/hygro). It COULD be a little hot at the tops, but I doubt it is heat stress causing my issues with brittle crusty burnt to hell fan leaves. It isn't very warm to my hand at the tops and there is good circulation. I also have fans blowing horizontally across the bulbs to blow that direct heat away a bit.

I have quite a visible algae issue on the top of the hydroton, but it does not extend much into the pots and the system is not slimy and the res water is not cloudy. However, this might be a problem right? I have since covered the tops of the pots with thick black plastic but this will most likely not fix the issue now... next time

I have read countless diagnosis helpers and threads about general growing and issues and I am really at my whits end with this current issue. I just flushed the system with rain water with a little epsom salt (only a teaspoon in 40 litres), emptied THAT water out and filled again with spring water which was PH perfect at 5.5, added a lower dose of nutrient than previously (half strength GHE - 320 ppm or so) and 24 hours later my ph is 6.2 and ppm is 280. If this leaf issue is indeed nute burn, then I wonder why my plants are eating overnight like that. I realise that about 5-10% of my system water stays up in the trough. Could this be wrecking every new reservoir I make? This last flush should have diluted that 5-10% rather well.. down to 5-10% OF that 5-10% .. and the problem still seems to be progressing with smaller newer bud leaves.

Any expert advice would be awesome. My issues seem pretty sensitive and deep. Almost like the more I am learning, the more I am penalised It seemed to go better on my very first grow as it goes with so many things

If I have left any crucial information out (hopefully not, looking at this wall of text) please let me know!

Bump? Help!

NFT is advanced from what ive seen, if you dont have the slope at the right angle the nutrient solution could be around the root system too long suffocating them? algae isnt good either it could cause root rot or other problems

From what I can tell, I have had few issues with roots at all, the reservoir is well airated and pumps through the system for 15mins every 15 or at most 30. So the exchange is good. The spinoff of that almost constant flow is the algae issue with top feed, but I don't see how that is causing a big problem as the whole system is slime free below the pots and the roots are healthy and white.

Perhaps it would still be best to try and increase the slope towards where it drains, but I wonder if there isnt also a unique issue with my strain (bubblegum - which is widespread and differs) and the nutrients it wants.. then there is also the specific seed the mothers come from. The one selected showed this leaf condition in its late flowering, in the same system as 2 other large plants that did not really. So it makes me wonder if it could just be something this particular pheno/strain wants. How to figure that out is mostly up to me I guess Or to try other strains, but most want the same thing and GHE's recommendations stand firm for many people. The problem seems to have slowed down in the last few days so perhaps I have solved it with NOT using lucas formula and sticking to GHE's chart. Hard to tell when alot of damage is done.

I might have also shocked these when they were little with a half strength dose of full on early flowering, not the starting dose for rooted cuttings I quickly corrected this though (within 48 hours of making the solution). I would appreciate any advice about safely moving little ones. I have a friend doing the mothers and we are moving cuttings directly to flower when they root. We have seen some impressive starts with high doses of nutrient AND some unhappy starts. It is all a bit in the air. Would it probably be better to veg them in the mother setup for at least a week maybe 2? Just to strengthen them a bit?

In ph is rising and ppm falling that means they are up taking the nuts and are hungry, you may try to increase nut level thought your so far into flower... I'm usually around 1000 ppm for flower. The yellowing of the veins shows a iron def. I think the brown upward curl could be phosphorus def. Or could be lock outs. Your starting with water that is 5.5 ph before you add nuts? The nuts will further drop the ph.