[KaLiB]

You can change the rockscape but avoid stirring up too much detritous as it could cause a release of nutrients into the water. I would suggest minimizing any re-scaping work as each time you re-scape you stress the livestock in the tank.

If you want to see a drastic change in No3, you will need a 40%-50% water change. It won't really solve the problem long term as water changes must be done consistently to keep No3 low.

It'll be better to attack the No3 problem by introducing means of dentrification rather than just purely water change. You can look into these methods:
- Use of a deep sand bed/Plenum(but will be troublesome for a tank already set up)
- Install a denitrator
- Use biohome filter media
- Using a protein skimmer
- Control feeding(feed what your fish need, don't feed excessively) and stocking levels(avoid overstocking)
- Get more LR