I had a local tide pool tank when I lived in southern California. I took marine biology classes through UCSD’s extension program, and thus was able to obtain a collectors permit from the state.
Instead of using Instant Ocean and mixing it with freshwater to create the salinity needed, I just took plastic Jerry cans down to Scripps Aquarium in La Jolla and used the filtered sea water from their huge public aquariums. We were permitted to do that back then. It already had the needed trace elements, and it was the actual ocean water used in their tanks and not artificial. It was free to anyone to fill us their cans.
For awhile, I had a heater in that tank and tried to keep coral reef fish, but found that so many of those species are so touchy about water parameters, including temperature and salinity, that it was hard to keep them alive. Feeding was another problem.
I also had a five-gallon mini marine tank in which I kept tiny dwarf seahorses, whose adult size wasn’t more than an inch or so.
That was my brief foray into saltwater.
I also had freshwater tanks back then, then went for decades without any aquariums until I recently started keeping them again, beginning in 2010. Now, it’s freshwater only, and no tropicals. Cold water fish are hardier and easier to keep.
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