You are posting similar questions in your other threads. Give the forum a little time and you can probably get your questions answered. You will difinitely need (2) Ray 2 to have the tank your describing though. One Ray 2 over a 75g will give you poor results I am sure.
Eco yields poor results with carpeting from what I have read. MG in your case is not a good idea if you plan to rearrange a lot. If your on a budget, it think your best choice is probably Safe-t-sorb. If you will be dosing the heck out of it, the charging of it will be high. It's fairly small in size and very uniform. It is light though but I can see HC growing in it. I use it for my growout and I will probably choose it for my Living Rm display tank when I set it up.
Unless your topping dirt, I wouldn't bother capping with sand on anything else. Capping flourite/eco really does nothing for they are substrates that can be used alone as is. Eco and flourite are not too expensive imo. That title belongs to Aquasoil. Safe-t-sorb can be bought at Tractor Supply for about 10-13 bucks for a large bag. It should take no more than 1-2 bags of it. I think I used 1.75 worth to give me 3" in my 125g tank.
Sorry for getting a little repetitive in my thread openings. I only have a few now, but every time I think of a new question and can't find a direct answer my first thought is a new thread because I'm varying from the other threads in topic. I will try and watch where I post my questions.
I read the same thing about Eco not being the best choice for carpeting. In my head I thought that the sand topper would really help the carpet spread, but I guess not. Safe-t-sorb sounds like a great buy based on what you said, and others are agreeing with you so it's definitely something I'm considering....I just wish it was darker.
I really appreciate your input...