I'm no expert, but 1 does seem a fair bit "chunkier" then the rest.
Got a bit of a new problem though.
I saw 1 of the shrimp cleaning away near the filter intake grill last night. He did look like he might have just been small enough to slip through.
I was thinking of buying some filter sponge to jam behind the grill to stop them getting in.
We don't get the heat you do their but I am planning to get a cooler, a fan when we get to spring if the shrimps do well. I don't know whether that type of cooler is available where you are and it may not be powerful enough anyway. I will just put it on the tank when needed, but thats unlikely to be often here, and so easy to set up. Obviously this isn't any good where you are based but I wanted to show an alternative to the chiller in case that suits?
Believe me when I say you don't want to go through the heartache of cooked shrimps, I am still gutted 6 months later and the new lot will never be the same????
CO2 and shrimps is very risky and so I wouldn't use it, especially if it isn't needed and everything is ok?