I'm relatively new to this and have had a saltwater tank since Sept. I started with a 29 gallon biocube in my office and it's doing great. I now have a 90 gallon at home and want to do my first water change after the first month. I have very clean ocean water from 3 miles offshore in the Florida Atlantic that has been stored for a couple of weeks. Besides some evaporation and increased salinity, is there an expiration date for ocean water? What about live things in the water that die from no oxygen as a result of storing it in a closed container? Maybe I should do an ammonia/nitrite test? Thanks.

I personally am not a fan of ocean water to begin with. You never know what you are collecting. You can not see parasites, bacteria, algae spores etc. However if you are willing to take the chance then you should certainly use it as collected or store it in a temp. controlled environment with a pump and some light. This is in order to prevent death which will cause a huge drop in PH and overall poor water quality.

the same day I collected ocean water earlier this week. I know a lot of people don't like water collected from the ocean. I get it when the water is really clear when I'm diving. So far so good. I'm at least 3 miles out near the Gulf Stream. Pollution is unlikely. Parasites? I hope never. It's fun seeing nice things appear in the tank like feather dusters. I think it comes from the water. I also collect the fish in the same water, so maybe there is some immunity for anything weird in the water. I'm new and learning.

Install a powerhead in the container your keeping the water in. This will keep the water for a good period of time. I've talked with people keeping it for a month.

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In your stored Ocean Water most of your animals will have died and will generate Nitrates, Ammonia and Nitrites in their decompositiion. Srongly aeriate tthe water and test for Nitrates, ph and Hardness. If your Nitrates are high or ph low, don't use the water. Ocean water from 3 miles out is not the same water that Coastal Animals (Aquarium Animals) are exposed to, some of the parameters can be much different.