Plastic Jugs' Effect on Water Quality?
 

After adding water to my tank, sometimes I notice that the phosphate levels increase. Would long term storage (>72 hours) of water in plastic jugs result in an increased phosphate level in the water?

Most likely, the issue is elsewhere, but a quick rinsing with some vinegar might help remove any buildup in the jugs. If you could wipe the surface a bit, that might help, too. I might check the phosphate level in the fresh water and in a sample of the saltwater if the problem persists. A TDS meter sometimes is helpful when measuring RO/DI, as well.

Is it possible, yes. Is it likely, probably not.

Test the water before, or as you put it in the jug and then again after whatever time frame you like. That should answer your question.

That somewhat depends on the plastic. Typically, food-grade high density polyethylene jugs that have vinegar, drinking water, etc... in them have very little in leachable plasticizers and other contaminants. Other plastics, particular colored ones, may or may not have mold release agents, plasticizers and other things that -might- include some organic phosphate.

A more likely source would be organic phosphates in the water itself that are subsequently metabolized by bacteria and released into the water as inorganic phosphates that a test will pick up.

I agree that mold release agents can be an issue, but they can't linger very long. I was assuming (a bad idea) that the plastic was rated for food and water storage. I used the plastic 5g jugs made for aquariums, and they were fine.