Even though both my main tanks have DSBs, I'm still not convinced they perform as the perfect nitrate reducers without some help from LR
and good circulation. I've simply seen too many bare bottom reef tanks with lots of fish and LR
*and* with zero nitrates. My belief is that the truth is somewhere in the middle and that good nitrate reduction occurs both in good LR
stocking combined with intelligent water circulation.
It's the reef tanks with enough sand to host a volleyball tournament and hide a full grown nurse shark that make me chuckle. Call me a MSB guy, or 'medium sand bed'. 4-5" should be plenty of depth to make nitrate reducing organisms happy and not contribute to the dreaded anoxic DSB
's work by creating a layer or 'zone' at a certain depth in the sand that is transitioning between low oxygen and no oxygen. It's this transition zone that accounts for nitrate reduction because the organisms that live there have to convert nitrate for energy vs oxygen. The reason sand is more popular than crushed coral is the fine sand creates this special layer at a more shallow depth because of it's greater density. You could, theoretically create the same effect of a DSB
with crushed coral, but you'd need a *much* deeper layer of it.
If you've ever left a bucket of mature aquarium gravel that's been taken out of an established tank outside in the sun for a few days, you can see this in action.
I'm also not hostile towards bagged, live sand for reasons I've covered elsewhere. Dry sand such as ooltic is much cheaper, but it's also very messy for several months upon set-up and will fill up your filters with what best can be described as soggy drywall paste. Live sand has little biologic value contrary to it's marketing, but it settles much, much faster than dry sand. Does this mean you can save some money by using dry sand with a layer of live sand on top to keep it settled? Yep....and if you are going with a DSB
use the finest size you can.
All this is anecdotal compared to the far more critical issue of nitrate reduction. I don't care if you are just housing African Chiclids, damsels, or a full reef. Low nitrate levels keep a healthier tank, indicate a healthy tank, inhibit algae and other organisms which destabilize PH
, and drastically reduce the need for water changes. We might not be able to make up our minds exactly what method is best for accomplishing this, but if having a stack of LR
on 4-5 inches of inert sand gets us there, who cares about the icky details??
I am not a fan of wet/dry filters unless I'm going to house a tank of 8,000 feeder fish, and even then a couple of Emperor back filters with bio-wheels are a lot less hassle. Same bacteria - same method of gas transfer. While I'm not opposed to wet/dry's or bio-wheels, I am convinced they aren't as efficient at nitrate processing as good old LR
and power heads, and as mentioned above might inhibit it to a degree. There is one thing about that wet/drys I seriously don't like, and that's their ability to rapidly speed up water evaporation and hence increase the need for water top-offs.