poorly seedling leaves, can anyone help me?

[dwcgardener]

Hi all,
My little seedlings leaves are dying back and I dont know why? and hoping someone can spot the problem and offer a solution.
Running in: DWC 4 gal pot, air pump, ventilation in grow room, temps range 18-26c, pH averaging 5.6, using advance3d nutes ph perfect: 7ml Micro, 7ml Bloom and 5ml calmag in last res change, ppm 426 with water at 126 before nutes. unfortunately lost my thermometer so cant give res temps.
Did originally lock out nutes when 1st leaves came out making leaves yellow and starve her for a little while.
Many thanks

 

[Roark]

Wish I could help. How's she doing?

 

[JM]

classic potassium deficinecy.. that said, you need to understand the cause... I'm not familiar enough with ppm levels to tell you anything... but I CAN say... res temps are CRITICAL... too hot and you get microbes messing up root uptake and usually root rot to follow.

 

[Truu]

Raise your ph up to 5.8 and bump up your PPM's to ~600 IMO.

 

[Muddy]

I'd be curious to know your res temp as well. When you say your pH is averaging 5.6 can I assume it's been lower at times? Even at 5.6 the uptake of K and mag is reduced. However, using pH Perfect adding pH Up can really screw things up. What is your water source? I assume the 126 ppm was before adding the cal/mag. If so that is right at the top end of what AN recommends. You may need to reduce the amount of cal/mag or completely eliminate it unless you see a cal/mag deficiency starting. That will also help to raise your pH. Only add enough cal/mag to set your base water to between 100 - 125 ppm before adding your nutrients. I found out the hard way in my RDWC system that an excess of cal/mag can produce symptoms that look very much like nutrient lockout.

 

[JM]

yes... cation balance is critical... I am with muddy and tru on this..