On the subject of etchants, I used to be able to get ammonium persulphate. It is incredibly soluble, and if you add more persulphate to the solution when it gets a bit slow, you can restore its speed. After doing this a couple of times, it will be found that crystals appear when the solution cools after etching. These are copper sulphate and ammonium sulphate. Discard these, heat up the solution, add a couple of spoonfuls of persulphate crystals, and away you go again. No waste!
The solution will keep a LOT longer in the fridge. DO NOT keep it in a sealed container, as it will give off oxygen and build up pressure.
I don't think the sodium salt is sufficiently soluble to do this recycling thing.