It's a little different because racking canes are acrylic but I'm sure they are similar in regard to this problem.
The mystery continues. I've now had the same piece of polycarb sitting in PBW for 21 days. I have to keep adding more tap water as it evaporates out of the cup. There has to be something very specific about some water supplies that cause it. At least we know that carbon filtering reduces the effect but I'm stumped. Carbon takes out organics.
FYI
I use Memphis tap water. This is artesian well water, very pure. They do add a lot of chlorine, though.
If carbon filtering helps, could this be a reaction between the chlorine and oyxclean?
My new glass should be in today. I'm sticking to hot water and a scrub brush for my BK from now on.
There may be a difference between chlorine and chloramine. I'm doing a side by side right now with some oxiclean and tap (chloramine) and some made from bottled water dosed with pool chlorine.
I wonder if the mystery reaction is somehow causing the exposed side of the material to expand or contract?
No, I think the plasticizers in the plastic are being depleted, leaving the plastic brittle. There are lots of different formulations used as plastisizers; this is what gives all plastics their flexibility. Plasticisers are not water soluble, so beer isn't going to accelerate their migration from the plastic. But they are subject to oxidative degradation, and this is what I suspect is causing the problem. Oxyclean is an oxidative cleaner. Probably heat exacerbates the effect.
I replaced my cracked and brittle sight glasses about 2 years ago (see this). I used to pump oxyclean through my BK overnight. Sometimes it would sit longer than that. I stopped doing that with my new sight glasses (Bobby's) and I haven't had any issue with them (they aren't as clean as I'd like, meh).
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