Photoperiod Yellow new growth during veg (RDWC)

[Boradan]

Having issues with my Cookies Gelato PHOTOPERIOD from Royal Queen Seeds.
Over the last few days, new growth has been turning yellow.

Strain: Cookies Gelato from RQS
Medium: RDWC (40 litres including reservoir)
Nutrients: Greenleaf single part Megacrop.
Additives: foliar spray of Epsom Salts at lights out. Greenleaf Calmag. 250ml Heisenberg tea every 3 to 4 days
Environment:
Lights: MarsHydro FC-E4800 at 25% and 18 inches (was previously 35% but there looks like some leaf cupping so I reduced it)
Air temp: 24c
Water temp: 22c
RH: 65%
pH 5.9
EC: 1.8


PH and ec have both been steady, so issues there (bluelab pH and ec meters, both cleaned and calibrated)

The Megacrop is a few years old, so I am wondering if there could be an issue with degradation there, so I am just about to change out the nutrients to Canna Aqua veg plus Rhizotonic. Also purchased the Canna mono iron supplement as it looks like iron deficiency to me (haven't used it yet)

 

[tronN00dles]

What’s your EC/ppm? Looks hungry to me.

 

[Boradan]

Sorry, updated the post
EC is 1.8 but was at 1.4 until a few days ago when I upped it in case of underfeeding.
Base ec of the tap water used is 0.4 (so mildly hard).
Recommended ec of Megacrop is 1.15 although it should be lower for RDWC as their recommendation is for soil, but this is also a PHOTOPERIOD so should need more than an auto.

 

[tronN00dles]

I’m surprised to hear a lower EC is suggested for RDWC. I’ve never grown in a recirculating system myself, nor with mega crop, but I do know at least General Hydroponics recommends much higher ppm’s for recirculating systems. Their Flora series recommends something like 1.2-1.6ec for soil but over 2.0-2.4 for recirculating systems.

 

[Boradan]

Odd. Roots in rdwc have 100% access to nutes so should need less concentration.
I am about to change the reservoir now to the Canna aqua line, so no second guessing (apart from strain/plant variation) as their chart is specifically for RDWC.
Hopefully this will sort any issues out...

 

[Boradan]

Just checked the Canna chart and I should be hitting about 1.5 ec, plus the .4ec from my water for 1.9 in total so my ec from Megacrop is about the same as canna recommends for their line.

 

[Boradan]

72 hours after switching to Canna Aqua Vega with some Canna Mono Iron, the difference is night and day:

Lots of green appearing at the base of the new growth leaves
The Picture below is the dame leaves from a few days ago and you can definitely see the yellow in areas that are now green.
Its even More noticeable on the largest fan leaf at the bottom - its now getting back to its full green It got significantly paler in the 2 days I was waiting for the Canna nutes to arrive..
Hopefully problem sorted now (I have also added a low solution of calmag to cope with that issue too.

 

[MrAutoGrower]

They’re lacking nitrogen. If you keep feeding calmag it will cause issues. Calmag is responsible for most people’s problems. When they see spots they assume calmag def and start feeding all sorts of calmag which then causes lock outs and so on. I never use calmag despite my water source having zero calmag in it. Most nutrient solutions have enough calcium and magnesium in them nowadays. Back off the calmag and feed a more nitrogen rich solution. Also check those roots underneath. If they look brown then it’s the start of rot. I see rot happening in these systems a lot. I’d defo invest in a root cleaner such as sensizym. Those kinda systems can get gunked up real quick, especially if they aren’t completely light proof which leads to algae growth in the res. Make sure they’re getting enough oxygen in your res too.

Open the res and take a picture of ya roots if u can bro

 

[Boradan]

They’re lacking nitrogen. If you keep feeding calmag it will cause issues. Calmag is responsible for most people’s problems. When they see spots they assume calmag def and start feeding all sorts of calmag which then causes lock outs and so on. I never use calmag despite my water source having zero calmag in it. Most nutrient solutions have enough calcium and magnesium in them nowadays. Back off the calmag and feed a more nitrogen rich solution. Also check those roots underneath. If they look brown then it’s the start of rot. I see rot happening in these systems a lot. I’d defo invest in a root cleaner such as sensizym. Those kinda systems can get gunked up real quick, especially if they aren’t completely light proof which leads to algae growth in the res. Make sure they’re getting enough oxygen in your res too.

Open the res and take a picture of ya roots if u can bro

Nitrogen deficiency affects the older leaves first though as it is a mobile nutrient. This was affecting only the new growth.
No root rot on the plant either - I dose on each res change (and every 3 days after that) with a Heisenberg tea made with unsulfured molasses, worm castings and TNC MycorrHydro.
Reservoir is light tight also and is aerated with 2 airstones and a Boyu SES-30 air pump (1800 litres/475 gallons per hour).
I also only used a very light dose of calmag as I foliar spray Epsom Salts. The necessity for calmag varies based on water/light/grow medium/nutrient line.
Just because your environment has enough calmag, that does not mean that everyone's does.

That is the plant now.

 

[MrAutoGrower]

Nitrogen deficiency affects the older leaves first though as it is a mobile nutrient. This was affecting only the new growth.
No root rot on the plant either - I dose on each res change (and every 3 days after that) with a Heisenberg tea made with unsulfured molasses, worm castings and TNC MycorrHydro.
Reservoir is light tight also and is aerated with 2 airstones and a Boyu SES-30 air pump (1800 litres/475 gallons per hour).
I also only used a very light dose of calmag as I foliar spray Epsom Salts. The necessity for calmag varies based on water/light/grow medium/nutrient line.
Just because your environment has enough calmag, that does not mean that everyone's does.

View attachment 1520561View attachment 1520562

That is the plant now.

It’s hard to nail it down to one answer. The more I see your leaves fading at the sides from yellowish to greenish makes me think of a potassium deficiency. It’s kinda similar. But usually when a plant isn’t green enough it’s lacking nitrogen. The first thing most growers do is up the feed when they see signs of hunger (yellowing). But it could be something as simple as a dodgy ph level. I see spotting on previous picture leaves which could be from toxicity or just a lock out/deficiency from the ph.

Edit:
You said you had the mega crop for a long time... that was probably what caused your problem man. They will recover no doubt if you’re feeding them some fresh stuff

Hope they turn out wel for ya