It's the Wet/Dry process that converts DOC (dissolved organic compounds = uneaten food and fish waste) to ammonia and then to nitrate and then to nitrate. It does not allow for the last stage of the Nitrogen cycle which is turning the nitrate to nitrogen.
That last step requires bacteria that live in an anoxic (oxygen free) environment. LR offers those areas in the deep recesses of the rock where there is little water flow. A DSB (deep sand bed) does the same in the layer below 4" (aprox).
That's why people are using LR rubble in place of bioballs. The LR rubble has some anoxic areas to help reduce nitrates while the bioballs do not.
A good skimmer and a refugium with macro algae can help quite a bit too.
If you decide to remove the bioballs, DO NOT remove all of them at once. The bacteria that break down waste to ammonia and nitrite live on surface of the bioballs, and you do not want to remove too much at once. Do about a 1/4 or a 1/3 per week as you replace the bioballs with LR rubble, or additional LR to the tank (slowly and only fully cured).
Hope that helps.