Nice pickup! It is possible for them to drown, recommended to keep them in water as deep as they are long especially at small sizes. Offer floating plants for him to rest/live on if u keep him in water that deep. You dont want to see him shooting to the top very quickly/erraticly for breaths of air, he should be able to breath comfortably and with ease. I aquired mine this year at 6" and was afraid to keep him in water that was 10-12" deep lol... He's still kept in a floating style tub at 12" and in 12" of water. They should be able to slowly climb or rest on the side of the enclosure for a breath without much effort. 1st. pic is his current setup at 12"...2nd pic is the 1st cple weeks i had him at 6" in a smaller tub. Mine has doubled in size in about 6 months so ull be able to upgrade him to deeper water fairly quickly.