Hi Bro, you can try polylab bio-sphere, you need to place it near your water flow area in your slump as its more effective with oxygen. That will be fastest and cheapest solution. Your No3 level is okay at the start, even mature tanks has it.. Not something that you need to be concern about..
Try to do abit of research on agale scrub, this is a long term solution to your worries..
Don't go get reactors for this.. It's a waste of money..
When you fish for love, bait with your heart, not your brain...