I did a comparison test a while back using LPCC diamond finish against USPCC Air Cushion finish. I put the card under running tap water for 5 seconds then dry it immediately. The test result showed that the water almost had no effect to the diamond finish, I might had rubbed off some of the coating when drying it off but the card is still very strong and didn't warped at all. The UPCC deck on the other hand, didn't hold up too well and as expected the graphite layer was visible on the edges.
Then came the fish tank, I thought lets try another comparison test between Serpentine - Emerald Finish, LUXX - Diamond Finish (both from LPCC) vs D&D Aviator Heritage - Magic Finish (USPCC).
This time I drop each cards into the fish tank and let it sink all the way to the bottom. it takes about 4 seconds (the depth is about 48 cm) and by the time I removed the cards, it should be in the water for almost 7 seconds. As I said the emerald finish did warped but that is about all, where as the diamond finish hold up very well.
Well for the Magic Finish, I don't think I have to say much. It was completely destroyed...
Anyway I didn't mean to go off the topic, I got to excited when you mention the fish tank