The large Homer Depot tupperware thingamagigs work.
A trash can with a tight lid and gholes drilled in the bottom works well for the tower, make it so that is barely fits inside the tupperware sump.
More sump= less refill for evaporation, you can also add another reservior under thwere fro sump top off water at a higher level than the sump or at the same level using a spectra pure electronic auto float switch and powerhead.
Or since you have a hard plumbed tank, turn the refill water on 2x a week etc. I'd say about 1200GPH at whaever head you are lifting the water up.
Use spray bars to make the movement even, generally along the lowest back wall right at the gravel line.
I'd use two spray bars 1/2 for each side and antisiphon holes drilled in at 45 degree upward so to produce some slight surface movement along with the surface skimmer.
The dIY reactor is a 3x 18 PVC Tune, with a drilled 3/4" elbow on the top and threaed or barbed lower outlet.
A 400-500GPH powerhead is used to drive this in the sump.
CO2 is fed into the powerhead's intake. CO2 rich water comes out the bottom of the reactor tube and should have a hose that directs the CO2 rich water directly into the suction side of the return pump.
You can add a 3/16" hole 10" down from the top and a piece of rigid airline tubing well glued about 1" long, 1/2 way in.
An airline is attached to this and also fed into the powerhead, this is a self pruging loop.
No one else knows about it for sump reactors or DIY externals.
A similar thing can be done with any external as the gas build up near the end of the day can reduce CO2 and flow.