[Michael Hoaster]

Yes, I think it is OK to use freshwater stuff. I've noticed some companies have started marketing their plant additives for marine applications too lately. I have used some, but generally, I prefer to use additives that are just one thing, rather than a combination of multiple things. That way you have more control over individual additions. I would think an additive with very small amounts of copper is OK. It's probably added to combat algae. Sensitive invertebrates may have a problem though.

I have tried several different root tabs. Honestly, I don't know if they helped or not. It's especially hard to know because seagrasses grow slowly, so when you add something, it takes around two weeks to see results. By then, you might think that something else has affected them. I will continue experimenting with them and report my results. I read that seagrasses prefer to get phosphorus through their roots, so the last tab I tried had a lot of phosphate. However, since fish food and fish poo already contain a lot of phosphate, and they settle on the bottom, it's probably not necessary. My strategy for this tank is to load the sand bed up with dirt and mud, so it is fertile from the start.

pH swings can be problematic so you need to be careful, but it's not rocket science. Bubble rates will vary for different tanks. It's been trial and error for me, but I bet there are some good online articles on ideal CO2 levels for fresh water planted tanks. So, you could probably find the ideal numbers to hit, and go from there.

I know some others have used Excel. I would guess it has bicarbonates, which are plants second favorite form of carbon.

Great questions, WYA123. Keep 'em coming!