Well, since nobody else is saying much, I will again give my opinion. Let me clarify myself just a little bit. I am one that pretty much agrees with everyone else on using the aragonite sand, big nice protein skimmers, etc., etc. I think that, if possible, that is the very best way to go. Buy the best. And, you should do it right the first time.
That being said, with me, it is generally not feasible to go that route. Many reasons, one of which is cost (actually, maybe the only reason, as most everything in this hobby can/is related to cost). Now that you know where I am coming from, I will move on.
First, about the P. Skimmer question, using a canister, I can not help you. Have never tried it or read about it where someone else has.
About the gravel, what kind of gravel is it, how big is it, etc.? When you say gravel, you are talking about gravel for freshwater aquariums and not a "crushed coral" type of gravel? When I think of gravel, I imagine 1/4 inch or larger pieces of rock. Just a quick question. Why do you want to use the gravel, other than having so much of it? Why put it on the bottom with sand on top? I don't really see how it could hurt, but I am sure there are reasons why you shouldn't. The only one I've read about is, the bigger stuff, i.e., your gravel, eventually migrates/rises to the top over time. But, I guess it depends on several things as to how long this will take to happen. I.E., how deep a sand bed is on top of it?
You know saltwater is higher in ph than freshwater which means it is basic (opposite of acid), so that it can dissolve/eat at certain things more so than just fresh water over time. So, I don't know much about your gravel, what kind of metals are in it, etc., might be a reason not to use it (I might also be talking out of my you know what, too), but it is just a thought.
Well, enough of my rambling. Maybe others can come along and give you some better answers/outlook on things.
Frank
That being said, with me, it is generally not feasible to go that route. Many reasons, one of which is cost (actually, maybe the only reason, as most everything in this hobby can/is related to cost). Now that you know where I am coming from, I will move on.
First, about the P. Skimmer question, using a canister, I can not help you. Have never tried it or read about it where someone else has.
About the gravel, what kind of gravel is it, how big is it, etc.? When you say gravel, you are talking about gravel for freshwater aquariums and not a "crushed coral" type of gravel? When I think of gravel, I imagine 1/4 inch or larger pieces of rock. Just a quick question. Why do you want to use the gravel, other than having so much of it? Why put it on the bottom with sand on top? I don't really see how it could hurt, but I am sure there are reasons why you shouldn't. The only one I've read about is, the bigger stuff, i.e., your gravel, eventually migrates/rises to the top over time. But, I guess it depends on several things as to how long this will take to happen. I.E., how deep a sand bed is on top of it?
You know saltwater is higher in ph than freshwater which means it is basic (opposite of acid), so that it can dissolve/eat at certain things more so than just fresh water over time. So, I don't know much about your gravel, what kind of metals are in it, etc., might be a reason not to use it (I might also be talking out of my you know what, too), but it is just a thought.
Well, enough of my rambling. Maybe others can come along and give you some better answers/outlook on things.
Frank