pH? Calcium? Light?

[plunker]

Hello all. This is my second grow, and after I pretty good first one I assumed the second would go just as easily. Silly me. Starting a couple of weeks in, one of the 2 plants developed brown spots on some of the older leaves which have only gotten (slowly) worse. I first thought it was a Cal deficiency and added some CalMag to the res, but that didn't seem to help much. Roots are nice and white with no signs of rot, and the plant seems to be growing fine, although it is quite short and dense. Lately I'm seeing increasing curl on the edge of some of the leaves. I've looked through the very helpful infirmary pics trying to match up what I'm seeing on my plant with pics of diseased plants, but am unable to figure out exactly what's wrong. Anyone have a guess what it might be, and what I can do about it?

California snow autofem, 4 weeks old, DWC, 4g Megacrop 2.0/gal, pH always between 5.5 and 6.5, but mostly between 5.8-6.3.

Res temp: 65-67F, Air 64-78F, RH 50-70%

Light: Atreum 100w at 24"

Thanks much!

 

[Simplicio]

It could be a CaMg need, over-feeding, too much light, or some combination.
If it's a CaMg problem, you might already have fixed it, but you won't know for a few days until you can see whether the new growth stays healthy.
4 g MC 1.0 is more than I'd be able to feed my dwc plants at that stage, and over-feeding is what I suspect.
After deciding whether the CaMg worked, give the plant less food and light for a couple days, and see how the new growth looks.
Increasing feed too fast, or too much light too soon, can also create problems.

Over-feeding will stunt growth.

 

[plunker]

It could be a CaMg need, over-feeding, too much light, or some combination.
If it's a CaMg problem, you might already have fixed it, but you won't know for a few days until you can see whether the new growth stays healthy.
4 g MC 1.0 is more than I'd be able to feed my dwc plants at that stage, and over-feeding is what I suspect.
After deciding whether the CaMg worked, give the plant less food and light for a couple days, and see how the new growth looks.
Increasing feed too fast, or too much light too soon, can also create problems.

Over-feeding will stunt growth.

Thanks so much Simplicio for your response! I did make one typo in my original post: the plant is actually 6 weeks old, not 4, BTW.

I think that pH must be part of the problem as well: just found out that BOTH my (low-end) pH meters were reading way too high. Looks like its time to spring for a BlueLab meter...

I've raised the light 6 inches, and have cut back the nutrients. My thought is to aim for about 400ppm (500 scale) of nutes. My tap water is 160-170ppm so I understand I should go for 560-570 total ppm. If I add CalMag, that adds an additional 200ppm, bringing the total closer to 770, which is where I have it now. Am I seeing that correctly? Could the 770 ppm be too much for the plant, even though the Megacrop part of it is only 400?

 

[Mr Green Fingers]

@plunker Looks like what I've had and am still battling, a phosphorus deficiency due to lockout as your PH was off, you need to callibrate these meters regularly like every week or 2 even if there Bluelab.
I've been adding pk 13/14 and keeping my ph at 6.2 and I'm getting on top of it but cant get rid of it totally yet!

Edit - actually you dont seem to have the bright yellow leave tips though so maybe it is only calcium lockout!

 

[Simplicio]

Your tap water could be the culprit.
I tried using my 190 ppm tap water once as an experiment, but my plants looked a lot like yours, so I went back to using RO water.
I'm not sure it was the water, because I was also trying a new fertilizer, but when I switched back to RO water and reduced feed, all was well.
RO systems can be cheap, maybe $50-70.

Most CaMg supplements also have some nitrogen.
You are correctly deducting you tap's ppm from the total, but the CalMag ppm needs to be added in.
Don't trust the bottle labels. Mix up a 1 gallon test batch of CalMag to see what additional ppm results.
I'm using MC 1.0 at the 6 week mark, and ppm around 500, with about 1/5 of that CalMag.

 

[plunker]

Your tap water could be the culprit.
I tried using my 190 ppm tap water once as an experiment, but my plants looked a lot like yours, so I went back to using RO water.
I'm not sure it was the water, because I was also trying a new fertilizer, but when I switched back to RO water and reduced feed, all was well.
RO systems can be cheap, maybe $50-70.

Most CaMg supplements also have some nitrogen.
You are correctly deducting you tap's ppm from the total, but the CalMag ppm needs to be added in.
Don't trust the bottle labels. Mix up a 1 gallon test batch of CalMag to see what additional ppm results.
I'm using MC 1.0 at the 6 week mark, and ppm around 500, with about 1/5 of that CalMag.

Thanks for the tips @ChroToker and @Simplicio,

Yowza! I did as suggested and added the mfg. recommended amount of CalMag (Mr. Mucha-Stash) to a gallon of standing tap water. The ppm went from 159 to 552! At that rate, there is no room for any MG if I want to keep ppms around the 500 mark.

I used the same tap water in my previous grow, but used the Flora trio with no added CalMag. Switched to MG 2.0 this time, after reading about it here and because I got the free 300g sample size. ;-) With this grow, I noticed a lack of Cal in newer leaves being too light green, so I added the CalMag. This cleared up the light green leaves problem overnight, and all was well for some days before I noticed the blotching in the pics above.

I think the right course of action is to start with a clean res, no CalMag, and MG2.0 at around 400ppm, with a pH of about 6 as determined by 2 separate meters, and go from there. Thoughts?

The plant is entering pre-flower, BTW, so there's another variable to add to the list. Planted at the same time I have an Alaskan Purple autofem growing in the same nutes/calmag/ph/tent/light, and it is thriving. So much fun! ;-)

 

[Simplicio]

Thanks for the tips @ChroToker and @Simplicio,

Yowza! I did as suggested and added the mfg. recommended amount of CalMag (Mr. Mucha-Stash) to a gallon of standing tap water. The ppm went from 159 to 552! At that rate, there is no room for any MG if I want to keep ppms around the 500 mark.

I used the same tap water in my previous grow, but used the Flora trio with no added CalMag. Switched to MG 2.0 this time, after reading about it here and because I got the free 300g sample size. ;-) With this grow, I noticed a lack of Cal in newer leaves being too light green, so I added the CalMag. This cleared up the light green leaves problem overnight, and all was well for some days before I noticed the blotching in the pics above.

I think the right course of action is to start with a clean res, no CalMag, and MG2.0 at around 400ppm, with a pH of about 6 as determined by 2 separate meters, and go from there. Thoughts?

The plant is entering pre-flower, BTW, so there's another variable to add to the list. Planted at the same time I have an Alaskan Purple autofem growing in the same nutes/calmag/ph/tent/light, and it is thriving. So much fun! ;-)

Now that you know the effect of CalMag, you might want to do the same for MC.
My MC 1.0 produces a ppm of about 128 when using 1 g in 1 Gal, and the liquid CalMag (Current Culture brand which also has nitrogen) yields 140 ppm per teaspoon (3 mL).
Right now my week 5 ppm is at 500, which I arbitrarily decided should be about 100 ppm of CalMag.
To get that I add MC = 400/128 = 3.1 g, plus CalMag = 100/140*1 tsp = 0.71 tsp ~ 3/4 tsp

I've read that LEDs can cause a CalMag need, and that seems to be my experience, but it's hard to be sure.
I'd recommend that you do use some CalMag, similar to the way I've described above, but MC 2.0 might have more CaMg than version 1.0.

Different plants have different requirements, but it's unusual for a big eater to suffer when the ppm is tailored to a light eater.
It is an underappreciated fact that overfeeding can stunt growth.

Changing out the reservoir is a good strategy when encountering problems.

 

[plunker]

MC 2.0 gave me a ppm of 130 using 1g in 1gal, and the CalMag gives 39ppm using 1ml in 1gal, quite close to what you got.

I'm going to change out the reservoir on this plant again, this time using 3.1g/gal of MC 2.0 and 2.5ml of CalMag as my baseline. This should get me close to 660ppm including the tap water ppms. I'll run that for some days and see if things improve.

Do you top off with plain pH'd water between changes, or do you use 1/4 strength nutes?

Thanks much!

 

[Simplicio]

MC 2.0 gave me a ppm of 130 using 1g in 1gal, and the CalMag gives 39ppm using 1ml in 1gal, quite close to what you got.

I'm going to change out the reservoir on this plant again, this time using 3.1g/gal of MC 2.0 and 2.5ml of CalMag as my baseline. This should get me close to 660ppm including the tap water ppms. I'll run that for some days and see if things improve.

Do you top off with plain pH'd water between changes, or do you use 1/4 strength nutes?

Thanks much!

I always top off with the amount that will make the res stay at the ppm I want.
This is probably overkill, because ballpark amounts are usually OK, and others have offered simpler methods, but here's what I do.
I have 2 reservoirs that hold 13 usable gallons each.
If one of these reservoirs were 1/2 gal low at 480 ppm, and I want it at 500, then I'd do these calculations:
Additional ppm = (ppm to raise to 500) + (ppm for the missing 1/2 Gal) = (20*13) + (250) = 710
To get that, MC = (710 ppm)*(1 g/128 ppm) = 5.5 g
This doesn't include any CalMag supplement, but it would be easy to do the calculation for 20% of the ppm being CalMag.

 

[plunker]

I always top off with the amount that will make the res stay at the ppm I want.
This is probably overkill, because ballpark amounts are usually OK, and others have offered simpler methods, but here's what I do.
I have 2 reservoirs that hold 13 usable gallons each.
If one of these reservoirs were 1/2 gal low at 480 ppm, and I want it at 500, then I'd do these calculations:
Additional ppm = (ppm to raise to 500) + (ppm for the missing 1/2 Gal) = (20*13) + (250) = 710
To get that, MC = (710 ppm)*(1 g/128 ppm) = 5.5 g
This doesn't include any CalMag supplement, but it would be easy to do the calculation for 20% of the ppm being CalMag.

Just to follow up and close this out: It has been a week, and the plant is doing well. I followed the feeding recommendations and kept the ppms (and pH) where they should have been. The help I received here is much appreciated!