Help! Some leaves looking bad

[whipsilk]

I'm a first time DWS grower with three plants nearing the end of their second week of veg growth. Some of my lower leaves on the two healthiest plants are looking strange, with yellowish spotting, but top growth is good. Here's a pic of the whole plant:

And here are closer pics of the worst leaves:

First, can any of you helpful people identify the problem? Second, what is the solution to save my plants and get them back to full health?

I'm using Sensi-Grow A&B, with Voodoo Juice, B-52, and a small amount of SensiZym (first week for this). My lighting is a 400w MH, about 18 inches from the top of the plants. My humidity tends to be on the low side (about 20%) when it's cold out, although I'm using a humidifier. Temp is also pretty variable - up to the high 70s when the light's on, but down to 60 or so during the 4 hours with the light off (I use a 20/4 cycle).

I change the water (heavily filtered and stands for 48 hrs., but not RO water) weekly, with the first day being a 'flush' of just water, nutes added the second day. They get lots of fresh air - the door is open with a smallish fan in it that blows on the leaves, plus the fan in the humidifier and a high-powered exhaust fan.

I also keep a bowl of filtered water under the light to help the humidity. I've had about 4 gnat-like fliers drown in it, although I haven't seen them outside the grow room and have no idea where they came from. Are these anything to be concerned with?

Happy to give any further info if you need it - and thanks in advance for your help.

 

[Green Knight]

I think it might be nute burn to be honest mate (if you look at the very edges of the affected leaves they've burnt and shrivelled in). 20% RH is also very low (60% or thereabouts is more ideal in veg) so you're on the right lines trying to increase the humidity.

The new growth looks healthy though which suggests the problem is fixed (the affected leaves will never get better, just keep watching the new growth and this will tell you if the problem's sorted)

What's you EC / ppms - do you have a meter out of interest?

 

[whipsilk]

Hey Green Knight - Thanks for the quick response. I certainly guess it could be nute burn - I know to start very low and work up. The manufacturer recommends, for my tank, 2 oz. I did .5 oz. last week, and 1 oz. this week, and would normally max at 1.5 oz. starting next week. I had thought that might be low enough, but maybe not. I'll try another 1 oz. (half the recommendation) for week 3, then maybe go to 1.5 oz. for week 4.

The humidity situation is frustrating; I have a humidifier running, a bowl of water next to the plants for evaporation, and still can't get it much above 20% on really cold days; when it warmed up to the 40s and 50s last week, my humidity soared to around 40-50% in the grow room.

Sorry, I don't have a meter to measure ppms, but I just ordered one. I'll take the measure later this week and post it. Thanks again for the advice; if you have more, I'd love to hear it. I will keep watching the new growth though.

 

[Green Knight]

No worries mate. From my experience manufacturer recommendations are often a bit too hot - are you going off the bottle or a specific schedule? (And are you growing a regular or an auto - if it's an auto they are very very sensitive to nutes, easy to burn them).

I use Canna and have never got anywhere near what's on the back of the bottle (they say 40ml per 10l for instance, the most I've got up to to date is 25ml per 10l). I use an EC meter and check it daily - if the EC/ppm increases the plant is using more water than nutes so I lower the nutes, if the EC/ppms drop I increase the nutes because the plant is using more nutes than water, and if stays steady then it's spot on. I adjust until it holds steady as a general rule. An EC or ppm meter will give you a really good understanding as to exactly what the plants are doing in terms of nutes, and whether they need more or less.

That's a bugger about the RH, not sure what to suggest really as it sounds like your doing everything you can to raise it. Have you got a fan running for extraction? You could try putting that on a timer so it's not running all the time and allows the humidity to build (like 15 mins on, 45 minutes off or something), or try putting an air stone attached to an air pump in the bowl/bucket of water - that will be more effective at increasing the RH than the bowl of water sitting there alone. As the plants get bigger they'll transpire more and more water into the atmosphere so the RH will increase.

 

[Cultivator]

i have to disagree. that doesnt look like nute burn to me. it looks more like a ph issue.

so u are growing dwc? ph@5.2 it should raise up to around 6.3 with sensi grow and that will give u the full range of ph.

Hey green, its strin and grow dependant. but i usually use alot more than the recommended dose in flower, pushing ec as high as 2.6 at times. but in veg ec of 1.2-1.4 is more than enough for an indoor plant.

 

[Green Knight]

Lol, I give up C! It's clearly not my night!

 

[whipsilk]

Thanks both Green Knight and Cultivator -
First, on the humidity - I do have an air stone with a pump in the tank (I didn't think DWC would work without it); I also have a pretty heavy duty exhaust fan running while my light is on so there's a good amount of fresh air/air exchange. The heat in the grow room never gets above 79 degrees. Maybe I shouldn't grow during Jan/Feb since the cold outside tends to keep the humidity low inside. The strain is Blueberry (not autoflowering). I'm encouraged, though, that it doesn't seem to be spreading up to the newer growth.

Cultivator, would Blueberry need that much nutes? I've read quite a bit and most advisors (including the hydro store seller who helped advise me, and who sold me the nutes) recommended I keep the nute level low, going no higher than 75% of the manufacturer's recommendation, even lower for the first two weeks of veg (so I used 25% in week 1, 50% in week 2). I've seen those recommendations pretty consistently for Advanced Hydroponics products. I'll have my ppm gauge in a couple of days, and measure it (and post) with a report on their progress.

I worried that it might be a pH issue - I hadn't bothered with pH measuring since the Sensi-Grow is supposed to be auto-adjusting and pH meters are a pain - the automated ones are apparently very temperamental; I have a manual set, but I really hate playing that 'guess the color' game - it seems so uncertain and vague.

 

[Green Knight]

Sorry whipsilk, I meant to also put an air stone in the bowl of water that you've got sitting near the light for humidity. The bubbling will help evaporate more water and increase the humidity more than a bowl of water on it's own (but it might be worth moving it a distance from the light because it could splash). You're right, DWC wouldn't work without an air stone.

If your fan's heavy duty that will also explain the low RH as you're extracting any humid air and replacing it with the dryer air from outside - if the air exchange is that good you'll never raise the humidity if its a low RH outside. Can you turn the fan down or put it to a timer to allow the humidity in the tent to increase?

Always good to have a pH pen and an EC meter if you're doing hydro mate. They're basically a prerequisite if you want to keep issues and problems to a minimum and whilst pH meters can be a bit delicate and need regular calibration it's much easier than trying to fix and diagnose problems with your plants at a later date. The liquid testers are better than nothing though

 

[Cultivator]

I cant say exactly how much nutes ur plant needs as all grows are different. thats where an ec/ppm meter comes in handy. then u can start at a lower strngth and push it till the plant starts to show a tiny bit of nute burn then back off a touch. but in veg ive never grown a strain that needs higher than 1.4ec.

 

[Cultivator]

oh and u need to get that humity up.

its a calcium def by the look of it. do u add cal/mag. if ph is too high it will lock out but could be that u need to add some.