Wet/dry biofilters, Live Rock, and Scrubbers

You don't "need" wet/dry biofilters, and you really don't "need" live rock either. They are not requirements like oxygen is. However they are backups, which always are working, especially on ammonia, and they are also always working in-between scrubber cleanings. Without LR or sand, or without a bio filter, you would need to pay special attention to always having lots of algae growth on at least one scrubber screen when you cleaned another screen. And most people don't have more than one screen, so there is no option. Also if something happened to your scrubber growth, you'd be in trouble while waiting for new growth to occur.

The wet/dry is a powerful ammonia remover, but if you have lots of sand you should be ok without it. A wet/dry (also called an ammonia tower when built large enough) is most useful in retail where the tanks have no rock or sand. Wet/dry's do makes lots of nitrate, and do nothing for phosphate. LR and deep sand beds do handle some nitrate, but do nothing for phosphate (except become a temporary sponge for it). Skimmers and GAC don't remove any ammonia at all.

So there is no biological need for a wet/dry or for rock/sand, but you will probably always want one or the other.

Thanks SM, I have been thinking about removing all my LR from my sump and just have LR in DT. I'm also going to make a second scrubber. I am cleaning my scrubber every 14 days, but it does take a good 5 days to get some solid growth.
Cheers Ben

This is why I like a lot of Live Rock in my SW tanks and a Bio wheel in my FW tanks. I have also noticed that the Aqua Clear filter with the sponge do a great job of handling ammonia and they also seem to handle nitrate as well. I think the slow flow of water through the sponge makes anaerobic bacteria that help consume the nitrate. I have no way to prove this but I have a FW tank with the dual bio wheel and another with the aqua clear and they are stocked similar but the aqua clear tank always has a lot less nitrate and only needs water changes about every 3-5 weeks as the bio wheel tank needs it every 1-2 weeks.

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I think the slow flow of water through the sponge makes anaerobic bacteria that help consume the nitrate.

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If you have any flow through it, it aerobic.

The sponge is about 3" thick and the water pours on top of it so I am not sure how much flow it has at the bottom. It sets against the bottom and the sides are tight to is as well. There is also a sock of carbon over the top of the sponge as well.
I have thought about taking four 50 foot rolls of the flexible 1/2 pvc and filling them with crushed coral then very slowly pushing water from my FW tank through them. I am talking about just a drop or two per second going through all four 50 foot tubes. This would be water that would pass through a few different descending stages of media so the crushed coral would not get blocked to fast. I am sure after a dozen or so months it might start to clog and each line would need to be purged or replaced with new crushed coral a month of two apart. I figure after making this long trip there would be anaerobic bacteria to eat the nitrate.
Of coarse this is all for not if I can dial in a FW scrubber to do this work instead.