Rust spots in RDWC

[GenghisChron]

Not new to growing but can't seem to get a handle on this plant thats 23 days old now. This is my first grow using mega crop and I've been using @Mañ'O'Green feeding chart. Plants germed and sprouted without issue, since about day 7, rust spots have been showing and slowly spreading on fan leaves. At the time, I already had a weak nutrient solution in the res that consisted of 100ppm of calmag and 270 ppm total with MC 2 part. This looked to me like a calcium deficiency. I changed the res on day 12 and added 150ppm calmag 110ppm partA 150ppm PartB with humid and Hydroguard...total ppm of 410. The rust spots continued to happen. On day 20 I changed the res again. I upped the Calmag to 220ppm 130ppm PartA and 150ppm PartB with humid and Hydroguard total of 500ppm. The rust spots are still spreading.

What originally looked like a calcium deficiency is not slowing down by adding calcium to my mix so any advice would be very much appreciated!

I'm using RDWC. Plants are in 8gal buckets with a 40gal reservoir. Total water volume of 40 gallons. Each bucket has 2 bubblemac stones being pushed by a 1300GPH air pump. Also using a chiller maintaining water temps of 69 degrees.

Im using MegaCrop as mentioned above with RO water. Starting ppms are 0 and pH is kept between 5.9-6.1

Strain is Strawberry Cheese from HGCC and is 23 days old today

Daytime temps range from 71-73 degrees and 52-55%RH. Nightime temps 66-67 degrees and 55-56% humidity

Im using a Scorpion Diablo from HLG in a 4x4 Gorilla tent. Light is 4 feet above canopy at 60%

 

[Orion]

Your mc ppm might have been too low. Your said you started with 270ppm, 100 being cal mag. Later you upped the feed ppm to 300.
This might still be too low.
I wouldn't add calmag. When this happens to me, adding cal mag doesn't seem to help. Mc should have everything your plant needs. I would play with your level of feed before adding another product into the mix.
Maybe do a water change and leave out the cal mag, then try higher ppm of mega crop
@Mañ'O'Green is quite knowledgeable about this stuff.

 

[GenghisChron]

Your mc ppm might have been too low. Your said you started with 270ppm, 100 being cal mag. Later you upped the feed ppm to 300.
This might still be too low.
I wouldn't add calmag. When this happens to me, adding cal mag doesn't seem to help. Mc should have everything your plant needs. I would play with your level of feed before adding another product into the mix.
Maybe do a water change and leave out the cal mag, then try higher ppm of mega crop
@Mañ'O'Green is quite knowledgeable about this stuff.

I was getting some slight clawing which made me think the feed was a bit high...at least the nitrogen part. It has since gone away. Also, the water level is dropping to the tune of a little less than a half gallon/day for 4 plants. pH and ppms have remained constant. From what I understand for DWC, this is ideal?

 

[Mañ'O'Green]

@GenghisChron Welcome to AFN What chart of mine are you following because that is all out of whack. Unfortunately some peeps took some of my spreadsheets and altered them and they are all fooked up!

MC is inherently out of balance until you reach about 600 PPM. This is what you should be running in 40 gallons.

Start with 5g of cal-mag in your RO water then part a mix well then part b mix well then add the rest of the cal-mag mix well and PH to 5.8.

For Bloom It works best if You have NPK Industries Raw K, P and Vitamin B (Mg) and get some soluble Calcium Sulfate (Gypsum)

Tag me in later and I will give yo a formula for bloom.

 

[Mañ'O'Green]

Ps Your daytime temps are a little too low. See if you can get them up to 78°F - 80°F

 

[GenghisChron]

@GenghisChron Welcome to AFN What chart of mine are you following because that is all out of whack. Unfortunately some peeps took some of my spreadsheets and altered them and they are all fooked up!

MC is inherently out of balance until you reach about 600 PPM. This is what you should be running in 40 gallons.

View attachment 1435361

Start with 5g of cal-mag in your RO water then part a mix well then part b mix well then add the rest of the cal-mag mix well and PH to 5.8.

For Bloom It works best if You have NPK Industries Raw K, P and Vitamin B (Mg) and get some soluble Calcium Sulfate (Gypsum)

View attachment 1435362

Tag me in later and I will give yo a formula for bloom.

Thanks for the reply! I must've had one of those corrupted charts because those numbers are far from what I was using. For the calcium I'm using general hydro calmag (liquid). You mentioned using 20g for 40 gallons, is that dry or wet weight?...what does that equate to ppm wise?

Is the gypsum you linked, a replacement for what I have? Thanks so much for taking the time to help! :smoking:

 

[Mañ'O'Green]

Thanks for the reply! I must've had one of those corrupted charts because those numbers are far from what I was using. For the calcium I'm using general hydro calmag (liquid). You mentioned using 20g for 40 gallons, is that dry or wet weight?...what does that equate to ppm wise?

Is the gypsum you linked, a replacement for what I have? Thanks so much for taking the time to help! :smoking:

My measurements are based on GreenLeaf CalMag Pro. If you look down the sheet all of the numbers are there under EC Hanna

ca 1300
Mg 840

so 2140/40 gallons or 53 PPM in the tank.

In bloom we need to add more Calcium without adding Nitrogen that is what the gypsum is for.

 

[Jovinn]

I had very similar spotting, suspected a Ca problem for a long time. In my case it turned out to be light stress. Not saying that's what it is (I definitely agree you're underfeeding), but worth considering. For some reason it masquerades as a calcium deficiency, but doesn't improve with adding it. Messed me up for too long, now I paranoidly see it behind all these unresolvable "CA deficiencies". But since you're using RO water, you very well could be calcium.

 

[Mañ'O'Green]