I would ask, why do you want a deep sand bed? You can keep a very effective Clean Up Crew in 0"-2" of sand, in my very non-expert opinion. If your only concern is to keep a "clean" sand bed with little maintenance, less sand would be easier, in my opinion.
If you're exploring using a Deep Sand Bed for denitrification, and without debating the efficacy here, consider adding a DSB to your sump, assuming you have one, and not your display tank. This way, you'll get the suggested/hopeful benefits of a DSB, but if for some reason it goes south, it would be much easier to remove it from your sump area than your display tank. Just an idea.
Definitely tagging to see what others think here :)
The idea is to use it for denitrification. I really don't know how well it would work for a saltwater tank, but my results with a deep substrate in my freshwater tanks were extremely positive, so I thought it would be worth giving it a try. Plus, since I know very little about this, I've been going through every guide out there, and most of them said that if your substrate is shallow and coarse you have to siphon it every now and then and that fine sand is "cleaner" but doesn't go well with creatures that require more water movement (which I might get eventually), so by elimination I thought it would be better to have a deep sand bed with a fine bottom and a coarser top where waste and leftovers could be processed without causing nutrient spikes or me needing to clean it lol
I won't be able to set up a sump system at the moment, any filtration has to happen in the tank or with a portable hang-on-the-back system. That's mostly why I though a deep substrate would be a good idea, provided it works. HOB filters have given me mixed results with my freshwater tanks in the past, while a deep substrate + good media for biological filtration gave me very steady parameters. Since I can only have a HOB in this tank for now, having a substrate that can handle some of the waste feels like the safer choice. But to be honest I don't know enough about the ecology of a saltwater tank to know if it would work in the same way.
Just to give some context on the tank and my current situation:
I was freshwater-only up until a week ago, when had the opportunity to "inherit" a saltwater set-up. A man passed away and his family didn't know what to do with his tank, so they were giving it away to anyone who could pick it up but were finding it hard to find someone and the fish were starting to die, so I decided to give it a go.
The setup was this 65g tank, a 20g tank used for his top-off system, a LOT of live rock, bunch of equipment (there was a big protein skimmer inside the tank, but it looks very worn off and I don't know how well it works so I'm not counting on it for now) and two yellowtail damselfish. Originally there were some corals as well, but they died while his family was trying to give the set-up away.
I'm housing the fish and the rock in the 20g tank until I can figure out the best set up for the 60g, but this was definitely not a planned purchase, so I'm gonna have to upgrade things very incrementally. My main goal for the next few months is simply to have a suitable home for the two fish that are here, but since I do plan on upgrading things eventually, I wanted to get the substrate right to reduce the risk of having to re-do it in the future.
I'm getting a lot of good input though, many options to explore here. I'm really new to this side of the hobby so it's very good to learn how those things work regardless. If there's no benefit to a DSB I'll definitely go for a shallow one. Thanks for your answer!
