Do some collecting. Bring three 5 gallon buckets with covers to prevent splashing saltwater in your vehicle. Bring whatever equipment you feel comfortable with for collecting - mostly collecting seaweed this time. That might be snorkel gear, it might be old tennis shoes if you just want to get your feet wet, or it might be a long handled net if you don’t want to get wet at all. Look for green and red seaweed mostly. Sea lettuce, Ulva, a green one, is great. It is hard to kill and easy to grow. The bushy red sorts like Gracilaria and Agardhiella generally do well. I have found it best to avoid the brown seaweeds. They look great of the rocks at the shore, and they seem to quickly die in the aquarium. They can turn a good setup into a foul smelling mess quite quickly. I know that they can be grown, but I do not know how to do it. I usually get some reds and greens I have had before, and then an assortment of small bits of those I would like to try. Not much of any one kind of these. Some will grow. Some won’t. Small quantity is important so that those that die can decay without using up all the oxygen in the water and killing everything.
Saltwater Aquarium Guide on Sea and Sky
If you are fortunate enough to live by the sea you can take advantage of free saltwater, but it takes some work to make it safe for aquarium use. The first thing is to find clear and clean water. You can usually tell the quality of water by looking at it. If you can go offshore to collect water, when you run into a major current, (here we have the Gulfstream), the water is particularly well suited for aquarium use. If you don't have a boat you can still collect water for near shore locations, just take care to stay away from inlets, river mouths, marshes and the like. Water from the beach will be better than these areas usually because the water will be less affected by run off and freshwater mixing, but if you have to get water from an inland location, go at high tide and be sure to test the salinity at the time of collection.
Alaska aquarium replaces fossil fuel with seawater system - AP News
Several factors make monitoring a marine aquarium's pH level important. One is that aquatic organisms thrive only in a particular pH range, which varies from organism to organism. It is therefore difficult to justify a claim that a particular pH range is "optimal" in an aquarium housing many species. Even natural seawater's pH (8.0 to 8.3) may be suboptimal for some of its creatures, but it was recognized more than eighty years ago that pH levels different from natural seawater (down to 7.3, for example) are stressful to fish. Additional information now exists about optimal pH ranges for many organisms, but the data are woefully inadequate to allow aquarists to optimize pH for most organisms which interest them.
Aquarium Snails: Sea Snail Species and Aquatic Saltwater Snails