How old are these babies? They usually have to be a few weeks old at least before they contract coccidiosis. It's good you're getting the toltrazuril, that was recommended to me as well.
I have dealt with a really severe strain(s) of cocci before. Despite sanitary practices (sterilizing brooders, feeders, waterers, changing water daily and washing with soap regularly) and with preventative Corid dosing and treatment/drench doses at the first sign... I continued to lose chicks to it. It's always the ones you most want to keep!
Struggling to figure out where it was coming from, I finally tried an experiment where I just gave chicks bottled water from the start. No more coccidiosis.
After we moved, I tentatively tried the tap water here (city) and stopped Corid, what do you know but Decembers chicks didn't get coccidiosis.
My conclusion therefore is that it was coming from the well at the old place. When I mentioned this in a thread someone was like "Eww, sewage in your well", but it might not have been that. There was a pond nearby and Florida aquifiers often feed ponds. What if there was a backflow issue? I dunno but it's one guess. Probably would have needed a well specialist person to come diagnose it.
The few chicks I managed to save taught me a few things that might be helpful. One, temperature control. It usually hits during a stage where you're reducing heat levels. Problem is, the sickness makes them cold. I would often see one or two chicks fluffed up, alone in a corner while the other ran around happily, and I didn't realize that was an early sign to make a change. Even if you have to separate a batch of chicks to accommodate different temperature needs. When they're cold they stop eating. So keeping the needy ones warmer is important. Basically bring the heat lamp closer until they aren't floofed up anymore.
If they don't start eating and drinking again on their own, mix some sugar, water, and a little egg yolk (or substitute medicine for water, I usually did) in a syringe or dropper and either use the official method to get them to drink it, or my wimpy but patient method of just holding them (seated comfortably) and using the end of the syringe to lift the top of their beak just slightly and offer only 1 drop at a time, letting them close their beak and swallow on their own time before offering more. I am always scared of sending fluid down the wrong passage so I don't do it the official way.
The sugar helps perk them up and getting cuddled helps with their wacky temperature control. When you put them back in the brooder, if they're awake, set them next to the feed (under the light) and peck in the feed bowl like they're day old chicks again. Even if they only eat a crumb or two it's good for them to be trying. When they wake from their nap they may try again. I put a little water in their regular crumble to make a mash, as that's always more appealing to them than dry.
If the chicks are still eating on their own, that's a good sign. I try to give them probiotics from a good brand like probios, which tests for viability. Real yogurt with probiotics in it is good too, but double check the labels.
The thing to keep in mind with coccidiosis, if that's what they have, is that it's ripping up their intestinal lining, making them sore and poor eaters. In my experience it was the not eating that actually killed chicks. There are so many strains of cocci and the mode they cause death can be different, some can be more direct. I would avoid anything that can be harsh on the digestive tract. For that reason, I didn't give them electrolytes in the water, as the salt is very harsh on damaged tissue, and it's not advised by vets for other digestive disorders like ulcers. The feed should already have enough electrolytes in it to keep their systems balanced, IF they're eating.
