I'm growing some hot chilli's and they were coming on nicely. But now they are about five inches tall and the new leaves seem to be changing colour to more of a yellowish/green. They are watered often and are growing in my greenhouse. Do they need any type of feed and if so what would you suggest ?. Thank you.
Don't think you need to feed them until the fruits appear.
There is a product called 'Chilli Focus' that is a liquid feed, seems to be popular.
The main thing with chillis is to maintain a strict watering regime. They don't like sporadic treatment! Maybe water twice a week with the same volume of water. They don't mind going dry for a few days; they'd be used to that in their natural environment.
Stop watering them ... the surface of the compost should be dry. If you scratch out a little compost from the surface of the plant, from a couple of inches down. If the compost seems damp ... they are overwatered.
The so called experts I know barely water them at all and if they do it's barely a soupspoon's worth every other day.
It sounds as though you are making all the mistakes I made in my first year... it will all make sense after a couple of seasons.