Thanks, im in sw western Australia. Chicks temp seems ok, they have access to shade and seem to move between, that, sunbaking in a spot of sun or under the brooder. I have been also feeding them scrambled egg or pollard, yoghurt and honey mix on average of every 2nd day. But the starter is their staple (didnt want them to fill up on other and miss their meds in starter). Theres not really mozzies atm...and cant see anything obvious inside beak (but tricky to get a good look)....
Have you always given medicated starter?The chicks were from a breeder/hatchery (of several breeds). I actually have my own wyandottes that I breed and have never seen the persistent blood in poo or any of these issues really...mind you they're usually raised under a hen so always seem healthy and robust (these chicks were meant for a broody - who decided to give up the day they arrived).
They have plenty of room under the heat source - the 2 small chicks do spend more time under there than the others. Only one (in the first pic) is fully feathered (and huge) and I only have one heat source - so separating them at this stage isn't possible unfortunately. I'm planning on taking the large feathered one out once she has a buddy to go with (and they dont need heat) - although Im slightly concerned that they could be carrying something to pass on to my wyandottes.
Have you had any experience with Chronic Respiratory Disease (Mycoplasma gallisepticum)? Im wondering if it could be that? Apparently it can retard growth (according to google)....
More photos of the poop would be good.
The Coccistat I'm not that familiar with @Eggcessive or @casportpony may know more about that. I don't think there's any contraindications with using Amprolium with it like you have been doing, but the Amprolium water does need to be the only source of water they drink. If you are giving Amprolium, don't give any extra vitamins that contain B1 (Thiamine) until you have finished treatment. Any special instructions for the Coccistat should be on the label of the feed bag.
As for if they have CRD (MG) - generally you would see bubbly discharge from the eyes, weakness, coughing, sneezing and mucous from the nostrils. They would have symptoms.
I think if they are eating/drinking well and relatively active, I would just continue with what you are doing and wait to see how it goes. Sometimes you get failure to thrive with chicks. Since this is a mixed age group, it can be harder to tell about growth rate. One way would be to weigh each chick and track the weight over the next few weeks to see if they are gaining.