Using mine for the first time, with a 7 gallon plastic fermenter bucket and two 2L bottles. I started off putting two frozen 2L in, and the temp dropped about 15F overnight. The next day both bottles were about half melted, so I swapped out one for a fresh frozen and left the other as-is to melt completely. Since then, I swap out the fully melted one with a fresh frozen every 12 hours and I'm getting a temp drop of ~10F in a 78F ambient room.
I'm liking this, any discount for repeat purchases?