If the overflow from the biowheel is knocking bubbles back down into the tank, I would say leave it. I'm not so sure a spraybar would be any better, especially if it's disturbing the surface, then that would be nearly the entire surface gassing off CO2 rather than one area of disruption from the HOB splash or the gas off on the biowheel. It's all just speculation without a drop checker or monitoring pH drops. The best method I've found that includes an HOB and microbubbles, is a limewood diffuser (or glass) directly under an Aquaclear or Topfin/whisper style HOB. Many people claim the Biowheel will gas off CO2 too fast, but I don't remember anyone backing that up with solid proof from a drop checker, and I'm 90% positive I've seen people here pulling it off with great success. In any case, you'll want your bubbles rising in the path of the current and getting knocked around a bit to get the best results. The tank in the sig pic below is running two HOBs (aquaclear and red sea) on either end with a limewood diffuser under each (from two separate yeast generators) and achieves 20-30ppm for the first few weeks into the mix.
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