The first plant I ran looked great until week 4 or 5 of flowering, then it started yellowing as if it had N deficiency. I tested the runoff and noticed it was salt building up so I flushed with half strength until my ppms were in the range I wanted. To fix this issue I run a feed, feed, water schedule. This keeps the excess salts from building up.
I believe my nute issue is solved, but now this grow I seem to have a pH problem. About 5 days ago my plants in week 5 of flower started yellowing/ tip burning and those leaves eventually turn darker brown and shrivel off. I've been watering with approx. 1250uS/cm (~800ppm) at 5.8pH the whole flower cycle so far with a regular flush on the weekend, and now all of a sudden when I tested my runoff to find the problem, I read 6.5 on a majority of the older plants. WTF!
Old flower nute solution:
1.5 tsp. PBP Bloom soil
1 tsp. Liquid Karma
1 tsp. Unsulphured Molasses
1 gallon 7.8pH tap water
pH down to 5.8
This solution gave me 850-900ppm
This is what I gave them up until now with a 30% runoff each watering. I am now adjusting pH to 5.0-5.2 before feeding because when I feed at 5.8, the coco just stays at 6.2 and will eventually raise like I am seeing now. I managed to get the pH of the troubled plants back down to 6.2, but breaking passed that barrier is hard to do. I will try another 5.0 flush tonight. I also cut the molasses out of the feeding and am going to use 1 tsp. of CalMag+ instead. Perhaps my cation exchange is out of whack, although most people say not to use CalMag after a couple weeks in flower. I figured since my water is kind of hard, I didn't need it either. If the Cal-Mag doesn't help my problem, I won't continue using it.
Since I have to know how everything works and this problem is really annoying me, I won't stop until I figure out what I am doing wrong. It doesn't matter how much you read about something, things still fuck up and you have to correct them, this happens to be one of those times. I am about to get an RO filter for my water supply just to rule that out of the equation. The plants look so good in veg and through stretch, but then I screw something up and they turn to shit with a high pH.
I took one of the plants with a 6.5pH runoff and put it into a larger container so I could flood it. I poured my 5.0pH, 800ppm solution through the pot until it was totally submerged. After 10-15 minutes I took the plant pot out and measured the pH of the solution in the larger container and it read 6.1. However when I ran more water through the plant's pot and tested that, it was at 6.3. So I do believe coco buffers itself to a certain pH and breaking that buffer is a bitch. I did the soaking for three cycles and it finally measured 6.1. After this I stopped flushing. I am going to try again tonight to get it below 6, but am I screwed now? Should I just say fuck it and let them go the last few weeks with a pH over 6?
New flower nute solution:
2 tsp. PBP Bloom soil
1 tsp. PBP Grow
1 tsp. Liquid Karma
1 tsp. Cal Mag+
1 gallon 7.8pH tap
pH down to 5.3
This mix gives me 1100-1150 ppm
Sorry for the long post, I just tried to cover every detail. Here is a picture from the 3rd, 8 days ago. This is about when the yellowing was starting to get bad. The older plants are the middle and left side. The runoff wasn't measuring terribly high though, around 6.2pH at 900ppm. Then this weekend when the problem wasn't getting better, I measured again and it was 6.5. The younger plants started showing the very early signs, but I corected pH and now added some Cal-Mag to hopefully help. Something happened and I'm not sure what caused this. I will grab a recent pic tonight when the lights come on, but most of the fan leaves are gone now. The buds are still green and seem to be growing, albeit slowly. Any help or words of wisdom would be mucho appreciado! I don't want to go back to soil but coco is kicking my ass.
Edited by TBM, 12 June 2011 - 05:18 PM.