I couldn’t wait a few days for the replacement tubes so I took a chance on Amazon next day delivery after I saw very useful infos posted here.
Here is my very short experiment. I ordered this tube on Amazon and it worked very well since Sunday afternoon. It’s way to early to tell how long this tube will last but it seems to hold pressure well, very accurate and only $8 per 10ft

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I calibrated a few times before running the CaRx again. I’m using two small zip ties to tie the ends and they seem to holding up well. The whole thing took about 5 minutes to replace.
In case the link doesn’t work. It’s 3/16 ID x 5/16 OD or 5mm x 8mm silicone tubing.
I think the original tube is Pharmed BPT. You can get it here if you have time to spare.
Ideal for fermentation, synthesis, separation, purification, control systems, process monitoring, and protecting sensitive cell cultures....
www.usplastic.com
Good luck and happy reefing