I am just starting to look into aquaponics, and had an idea, but I'm not sure if it would work out. Here is my thought. If you had a large setup, would it be OK to use the sump tank as a swimming area?

In my mind I am thinking: above ground pool as fish tank, waist high grow beds, followed by a sunken pool for sump tank.

Any reason why it wouldn't be beneficial to swim in the sump tank?

Technically, no. We swim in lakes where there are lots of fish, so a swimming pool would be no different. Two issues I can see:

1. If someone goes in wearing some kind of chemical (hairspray, cologne, etc...) that could mess with the chemistry and/or fish.
2. If your sump tank is open to the sky, it will get a lot of algae. This might make swimming unpleasant.

What if there was a cover that was only removed while swimming? Since this would mostly just be used by my family, it shouldn't be hard to make sure all lotions, perfumes, etc. were removed prior to swimming. We have been tossing around natural pool ideas for awhile, and this seemed like it might be a decent possibility.

I don't see any reason not to make the sump tank serve dual purposes. You basically would be making a pond, rather than a pool, since you wouldn't want to add chlorine or any other chemicals usually used in pools. It sounds like you're looking at a really large set-up. Hope you'll post pics or links to a page where you document the project from start to finish. I'd love to see it!

The difference between this and a pond is that your nutrient concentrations will be 100x what they are in a pond (where oxygen is the limiting factor). That will make for a lot more biological life (like algae) than you'd see in a pond. Given that, I'd say that blocking all sunlight is pretty much required. You also might want to take a bath after, and avoid opening your eyes.

Per the NYT, the bacteria is good for you. There are other organisms and materials in there that might not be so good.