i used to have a crocea too. If u place it in between LRs, it will eventually stick on the LR, as in if u observe the bottom part, that will be some tissue growing and sticking itself on LR.
you can always screw in ur fan onto ur hood(cover). or get a teco mirco chiller. just the size of ur palm. Or u can get a iceprobe. that's many alternatives.
go c328 or sembawang shopping centre. they have solid betta. If keep neon tetra, just need a small hang on filter will do, no need air pump. my betta which has since retired. Cost, $1.20. cheap.
full tank pic.. having GHA. suspect is the daily topup of water without using anti-chloramine.. getting one bottle this afternoon.. kind of empty still.. one mth once shopping..