My experimenting is hitting a snag! Before you can do a comparative test you have to be able to keep the two tanks growing equally, when they are set up equally. I haven't yet been able to do this. One tank is doing better than the other. And, neither is doing as well as I want. So, I'm thinking about adding/changing some plants. One thing I'm learning is that having floating plants, at least when they are Salvinia minima, it takes a lot of attention to keep those plants from blocking all of the light. They grow very fast! I have removed all of it, except what is contained in small plastic rings. But, even with that I need to remove excess plants weekly. I wish I had some hygro polysperma, but it is illegal to ship into California. I'm watching for someone selling it locally.