I've metioned before that I've never had any luck with keeping shrimp when dosing with EC. It might have not been the EC but have tried a few times and they all die within a week.
I've stopped using EC now as I've got a co2 system and will be trying shrimp again in the future but in a different tank.
I dose a carbon suplament in my shrimp tank (daily recomanded dose, but one day a week lol) and use ferts with no problems, although you should watch out for your apple snails with ec or similar.
My invert and otto tank varies from 20'c to 28 during the summer (not a great idea to run at 28 if you can avoid it though). 18-25 is the usual breeding temperature with 24 being the best (IMO)