Hi Jimmy, I was going to use Instant Ocean but someone told me once that it was very strong and could irritate and even burn the terrapin’s skin and eyes. And the same person told me that the salt was in brackish water setup for fish was regular rock salt. This person is very knowledgeable in turtle but does not breed terrapins. I really don’t have any facts on this but pasted down information. If anyone has any first hand knowledge that would really help. Personally I have been using rock salt since as long as I have had terrapins and have had no problems. On the other hand several of my older female, which were in captivity for several years before I got them, had lots of problems when I got them. Mainly shell rot and minor skin problems. It took a long time to kill the shell rot but every since then I have not had any problems. The previous owner kept them in FRESH WATER. That’s my input, please don’t kill me for not have any real facts. Jonathan The Scute Moderator