Newbie help needed

First time indoor grow for me. I`ve got 2 Pineapple Chunks going. They are approx 2.5 to 3wks in veg under a 400w mh. I`ve been using a local store brand veg a/b. Instruction on the bottle say to put 5mls per 3ltrs water. Thats how i`ve been doing it and both plants took off really well. Plants get watered twice aday. 2hrs after lights on and 2hrs before lights off.
From reading on here im starting to think it might be from over watering. The medium is canna coco and that all.
one plant is looking really sick to me for the last 2 days. She fell over and was lying down about 5-6days ago. She looks to have stoped growing and all the leaves are drooping and some are getting spots on them.
Whilst the second plant seems to be going well in my eyes anyway. But she is starting to get these little brown spots on the leaves. Looks like rust stains.
I`ll try to upload pics so ppl can see what i`m talking about. Any and all opionions/sugestions welcome and appreciated.

This is the sick looking plant



This is the plant that healthier one



This is the spots in question on the 2nd plant

Looks like over watering.
You need to be waiting until not just the surface of the sol is dry, but stick your finger down and make sure the top inch or two is dry as well before re-watering.
I would try flushing the sick one, you might be experiencing nutrient lock out IMO looking at the spots and light green hue to the leaves.
If you've been feeding them at full strength that often with nutes, a flush and clean reset would be greatly beneficial.

Even that healthier plant is showing signs of moisture stress, whats your RH and Temp range in there?
How bout your air flow, are you keeping an oscillating fan going over the plants so they don't over-transpire?

temp gets to 74.2f at night and gets to 78-80f during the day. Humidity is currently 54%
I`ve got 2 oscillating fans running.

Anyone got any more ideas as to what I can do to save her. Flushed 2 days ago and today she seems worse.

Why do you need more ideas? Your over watering them. That little one is worse off than the bigger one because it cant take as much water as it. Think of how much they actually can drink. Think about it.

And the little ones in a wayy bigger container.....fail.

They are both in the same sized pots. They both got watered the same.
They both were the same size last week.
I now know that I over watered. Will she come ok if I start watering her every 3-4 days?