Autopot 1st grow again

All seeds sank and were placed into a 75mm cube of rockwool. 3 out of 4 seeds sprouted. CPK failed and was replaced with a LA Confidential. Seedlings were struggling (yellowing and slow growth) so I dug out parts of the rock wool and packed in some seed raising mix, Seedlings seem to improve a little and decision was made to place straight into the autopot container. Seedlings have continued to have a yellow color with little growth. This I'm thinking is from being in a over wet medium (rockwool) for too long. There's leaf damage to a couple of leaves(photos) The replacement LA.C seed was soaked overnight and placed into a jiffy disk. Seed germinated and was also placed into a Autopot container. This seedling is growing well and is a green color. Decided to water the three original plants with a seedling strength coco a&b solution with added Cal-Mag, pH to 5.85 and applied till I had a 50% runoff (is this to make all the coco coir to have the same nutrient consistently ?. Outside temperature has started to drop so a oil fin heater on a thermostat will be added with a small fan for circulation.