There actually isn't a DSB in the tank.. it is only 2" - 3", and the 3" spots being unintentional, created by both the engineer goby and the vortecs. I still think that I can get away without an RDSB, between the skimmer that we will have and the other nitrate reduction steps we will take.
We tried out Seachem's De*nitrate a couple of years ago. It is basically a pourous rock that works to allow aerobis bacteria to host on the outside (to strip the oxygen from the water passing through) and anaerobic bacteria to host inside of it, similar to how a DSB works. It is meant to be run in a canister filter or I believe also passively in a filter bag in a sump. We ran it in a canister filter and it worked quite well to bring down our nitrates. Since it is a rock, it never gets "used up". Our sumps have compartments for bioballs, in a bubble trap sort of configuration. I plan to fill those areas with the De*nitrate rock that we have. Actually, we have the De*nitrate Martix, which is the larger sized rock, that is rated for greater than 50 GPH, the smaller, standard size needs to be fed no great than 50 GPH, which while it worked fine in a canister filter that I could control, won't work how we plan to use it in our new setup. Luckily I have plenty of both since I was testing both last year.
We will see if it does a good enough job on our nitrates, combined with the skimmer. If not it is easy enough to add an RDSB to our sump (much easier to add later than it would be to take one out
). The one downside is that we are pretty much giving away/trading away all of the sand that we had collected up for the RDSB from tank teardowns around the Bay Area.. most of it being kept "alive" in two 100g tanks. So if I change my mind later I will end up having to collect/buy the sand all over again. One thing that many people overlook is that even though we may not have paid for this sand, it was far from free... between gas, @ 14 miles to the gallon in our Expedition, buckets and lids from HD for transporting and our time and back muscles to empty out the tanks and lug the full 5g buckets back and forth. After everything is said and done it would almost have been cheaper to just buy the sand from the LFS that opened up 10 miles down the road. But then we wouldn't have the "live sand" that we were after
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