Manganese def? Seedling in coco

[Cwmoore577]

So I’ve just started my 3rd grow and already seeing a bit of an issue. Unsure what the problem is, I’m still a bit inexperienced but I thought maybe manganese?

I have one Zkittlez auto (17 days from sprout) which is yellowing between veins a bit.
Pic here:

and one GelatOG auto (15 days) in a 2x4 tent that isn’t as bad, yet anyways.
Pic here:

My light is the BudgetLED 250 watt red spec and it’s dimmed half way on a 20/4 light schedule.

My temps are around 75°F and fall to 69-70°F when lights go off. Humidity does fluctuate, high of 80% and low of 49% in the last 24 hours. I try to keep it over 60% as much as I can but it does drop when I run the exhaust fan.

My medium is Royal Gold Tupur mix which is coco based and Ive been feeding once a day using RO water only.

I started them with...
5ml/gal CalMag (Cutting Edge Solutions)
1.25ml/gal GH FloraMicro
0.6ml/gal GH FloraGro
0.6ml/gal GH FloraBloom
(pH 6.1-6.2, EC 400-500, 250-350ppm)

Last 3-4 days I’ve given...
5ml/gal CalMag (Cutting Edge Solutions)
2ml/gal GH FloraMicro
2.5ml/gal GH FloraGro
0.5ml/gal GH FloraBloom
(pH 6.1-6.2, EC 600-700, 450-550ppm)

Last night I dropped the pH to 5.8 thinking that if it was manganese it may help.

Any suggestions?

 

[Listersmeghead]

Hiya, good ph range is 5.8 to 6.2,you're right around there, so dropping it might of been a good thing. There's not much I can see wrong with them.As long as you travel through that range of ph you should be good.
Sometimes it takes a couple of days for the colour of newer leafs to develop.
Keep an eye on them next couple of days and that drop to 5.8 should work.
Lastly the calmag 5ml/gallon is quite strong, I usually do 1.5ml per gallon, but some plants need more.

 

[Cwmoore577]

Hiya, good ph range is 5.8 to 6.2,you're right around there, so dropping it might of been a good thing. There's not much I can see wrong with them.As long as you travel through that range of ph you should be good.
Sometimes it takes a couple of days for the colour of newer leafs to develop.
Keep an eye on them next couple of days and that drop to 5.8 should work.
Lastly the calmag 5ml/gallon is quite strong, I usually do 1.5ml per gallon, but some plants need more.

Ok I’ll keep that in mind. Are you using RO water in coco when you use the 1.5ml per gallon? The 5ml is just what the cocoforcannabis site said the start with.

 

[Listersmeghead]

Ok I’ll keep that in mind. Are you using RO water in coco when you use the 1.5ml per gallon? The 5ml is just what the cocoforcannabis site said the start with.

I mainly do pure hydro,no I don't use RO water. Also, some calmag solutions are stronger than others, so it may be the case that's ok, it just jumped out at me that it was loads more than i use.

 

[Cwmoore577]

Starting to see these yellowish blotches as well.

Here’s the new growth.