RowaPhos is the best media for reducing phosphates. Put it in a reactor for best results. You can use all sorts of stuff to reduce nitrates, but essentially, you have 3 options:
- Grow a larger bacteria population to denitrify the nitrates
- Remove the nitrates
- Use chemicals
1. You can do this by increasing your LR and/or sand to provide more surface area. You can add reactors that knock about various media types that allow lots of surface area for bacteria to grow - although I'm not too sure how much denitifying bacteria will grow, as it needs to be in an envirnment which lacks oxygen (e.i. to mimic conditions deep in the rock or in a deep sand bed)
2. You can do water changes. Or you use algae to suck it up, then remove the algae.
3. Not a fan of this, as there's normally some horror story about most of these chemicals. Also, the other options are more natural and longer term solutions.