Robert Flory said:

I do quite well with DIY in a 55 with a difuser. I use to large 64 oz juice
bottles.

I have a 75 gal with a HOB filter, and use DIY CO2 injection.
Modified the spillways on the filter to reduce surface agitation.
With water of 4 kH, I get a drop in pH from 7.4 to 6.8.
I use a 64 oz juice bottle and a standby 1 liter pop bottle.
The reason it works so well is the DIY powered diffuser - couldn't get
an appreciable drop in pH with a static diffuser.

FWIW,

Greg G.