As long as the stream of co2 is getting to the mouth of the HOB return (instead of behind it) that should be fine. You could play around with it and see where you get the most efficiency. That being said co2 is cheap, so you could also turn it up more to compensate. In general co2 and HOBs aren't usually the greatest combo since co2 is lost by the surface exchange. Raising the water level of course helps but with an open-top you risk fish jumping.Thank you for all your help, that’s why I love this forum, you guys are so helpful. One thing I forgot to ask. My diffuser, I have it placed about 2 inches off the substrate directly below the HoB filter so the bubbles rise and then are moved around the tank by the flow of the filter. Would this be the best placement or should it be neat the front where the flow hits the glass before returing to the intake?
That rimless is calling out for a canister with lily pipes, but I understand if you don't want the added maintenance, etc.
Another thing I should point out is that tall tanks have small footprints. Which means you have less plant mass by volume. Because it doesn't have the small plant mass as a shallow tank, maintenance, feeding, stocking, lighting, etc becomes more critical.