All my larger tanks use External methods, mostly Venturis, they do the same thing as a disc, but require no maintance once set up. But they are more suited for larger tanks.
If you use a disc, place it somewhere the light does not hit it. Deeper is better, and in the flow/current.
That's not always an option and very often, out of sight, out of mind, so you forget and then CO2 goes to south..and then algae, then.....
A clogged diffuser adding CO2 vs a well cleaned one is the night day difference folks often see in tanks.
I can certain say even though the rate of gas being add is the same, you can see a dramatic difference in growth and pearling after cleaning them.
Excel will work also BTW.
A smaller powerhead can be hidden also and do the same as a disc also.
Regards,
Tom Barr