Regarding the deep sand bed....
The reason the sand needs to be that deep is to create an oxygen free zone, which can then be colonized by bacteria which break down the nitrates into nitrogen, which then diffuses away from the tank.
However, there are three huge issues with this.
1. It is very hard to establish an oxygen free zone, and you need a pretty deep sand bed to do so. It also takes months to established the oxygen free zone. This is why Kelz told you to increase your sand depth, and also why you shouldnt get anything that will stir the sand bed because it will keep introducing oxygen into the sandbed.
2. Even if you do manage to establish an oxygen free zone, you then have to have it colonized by bacteria who die when they are exposed to oxygen. This can take months, if ever.
3. It's super dangerous. The deeper sandbed will be colonized by other types of bacteria who will produce really dangerous compounds through their metabolism, like sulfur compounds. Which when released will crash your tank in a real hurry.
So if you still want to try a DSB, you need increase the depth and most importantly, make it so that it is remotely connect to the tank so if something happens (which it will) it can be disconnect from the system.
