HELP! Can't figure out this leaf problem. (DWC / Autos)

[TotallyJaded]

Hi everyone! Long time lurker, first time poster.

I'm in to my fourth week as a first-time grower (counting from the day I put the seedlings into the hydro system. All of the plants are autos, and all of them were drip-fed on a 6-minute interval every 8 hours for the first two weeks.

The nutrients are General Hydroponics Flora series, pH is consistently between 6.15 - 6.35. They're in a 4x4x8 grow tent, with ambient temperature at about 75, and RH between 40% - 50%. The lights are 2x Viparspectra PAR 600, all on, running 24x7.

For the past week and a half, the bottom leaves go crispy, and new growth is consistent, but eventually gets brown spots. My first thought was that I overdid it on nutrients (using 25% of the recommended amount from General Hydroponics). then I worried about root rot, so I've been using Botanicare Hydroguard for the past two weeks at the dosage recommended on the bottle. Then I tried moving the lights to 30" from the top of the plants (as recommended by Viparspectra) in case I was confusing root root symptoms with light burn.

I've changed the reservoir twice, and have been adding about a gallon of pH 6.0 water each day for the past three days. I've also checked for signs of bugs, but didn't see anything -- and really, I shouldn't. The tent is sealed, the intake fan starts with a carbon filter, and bugs in a basement in the winter are pretty rare here.

At this point, I'm stumped. I know I'm only a few weeks out from hitting flowering, so I'm hoping I can rescue these plants. Any suggestions would be appreciated!

[Toker1]

You have a deficiency. My guess it’s a PH issue. Don’t chase PH... but adjust to 5.5 then let it swing back up (over a 2-3 day period) to 6.5 before you adjust back down to 5.5. PH adjustments should only occur every few days. Maybe twice per week or so. PH needs to fluctuate between 5.5-6.5 to have healthy plants.

[TotallyJaded]

You have a deficiency. My guess it’s a PH issue. Don’t chase PH... but adjust to 5.5 then let it swing back up (over a 2-3 day period) to 6.5 before you adjust back down to 5.5. PH adjustments should only occur every few days. Maybe twice per week or so. PH needs to fluctuate between 5.5-6.5 to have healthy plants.

It'll be a week tomorrow since I've done a water change. Do you think I'm better off adjusting the water that's in the reservoir and leaving it for another week, or would you change it out with a mix that's balanced to 5.5?

In case it's helpful, this is what I changed it out with last week:

• GH FloraMicro: 2.5ml / gallon
• GH FloraBloom: 2.5ml / gallon
• GH FloraVeg: 2.5ml / gallon
• GH CaliMagic: 5ml / gallon (I'm using RO water)
• GH Diamond Nectar: 2ml / gallon
• GH FloraBlend: 2ml / gallon
• Botanicare Hydroguard: 2ml / gallon

[alltatup]

Hi Jaded, I would give the plants a 48 hour flush in pH'd water, and then add your nutes. I totally agree with Toker1 about letting the pH fluctuate between 5.5-6.5 (I'm hydro as well and I let the pH rise from 5.6 to 6.4, then I lower again. The plant absorbs different nutes at different pH levels.

[Toker1]

Agreed. Yes....A reservoir change can only help right now.

[TotallyJaded]

Thanks! I'll give that a shot. Somehow, I missed moving pH levels around in my research before I started growing.

[DW2]

Are the roots of the plants reaching down into the reservoir? If not, 6 minuets of water every eight hours is not enough. I use the GH Maxi Grow and MaxiBloom nutrients at the full recommended levels (GH RDWC schedule) and run a continuous water stream to the roots 24/7. The water needs to be well aerated and after the roots reach the water, an air gap should be allowed for the roots to take up oxygen as well. I, also, allow the pH to range from 5.5 to 6.5 and as Tolker1 stated, "don't chase it around". As well, block out ALL possible sources of light infiltration into the reservoir to prevent the 'brown' algae from growing, I even cover the net pots and Hydrotron pebbles with aluminum foil.

[TotallyJaded]

Sorry, I didn't get a notice when you responded. So, I flushed the water, did pH 5.5 for a couple of days, and all but one of the plants are looking better. Oddly enough, the one that's doing the worst is also the one growing the fastest. It's easily 3" taller than the other plants, huge stem, but the leaves seem to die after a few days. the roots in the air gap region of this plant seem a bit brown, so it looks like the Hydroguard isn't helping out there.

I changed out that water and did a new mix of 5-5-5 ml/gal (micro / flora / bloom) with 2mg/gal CaliMagic and 2ml/gal Hydroguard, pH'ed to 5.5. A few tips are showing a teeny bit of yellow, but nothing alarming.

The roots are all submerged in the reservoir, and have been for 2 - 3 weeks. Once I confirmed that they were all touching water, I stopped using the drip system. The reservoir has a 17 gallon capacity, and I've been running it with 13 (recommended by GH), so the gap is probably 2", maybe more. I also have to medium air stones going 24/7.

I was a bit confused on the drip system, since this transitions from drip to DWC. The 6 x 3 schedule seemed to get the roots into the water, but compared to pictures of other autos I've seen, it looked like mine took longer than usual to really take off. To be honest, I thought I was overwatering. Is 24/7 safe for seedlings?