How is the 75g going to be stocked ?
I've got 5 Aquaclears. They work very well for me.
The AC110 has a ton of flow and a very large media basket.
The only other HOB I would suggest is the Tidal 110. The Ken's Fish site has them on sale for $62, which is the least expensive you will find...
Amazon and Chewy has the Tetra AP150 air pump on sale for $11.xx.
They usually sell for $34-$40 I believe. 1 or 2 of those would be great on a 125g.
I agree with JayH, Swiss Tropicals has an awesome selection of foam sponge procducts.
Another option for sponge filters are the Hydro Sponge...
Couple of questions.....
What is your water change interval and about what % is removed/replaced each time?
Is the substrate cleaned with a gravel siphon vac at each water change?
Why was the foam sponge block replaced for the Aquaclear?
I agree with JayH....
Dr. Novak style plenum for the tank and throw in a couple of Biocenesis Clarification Baskets in the sump.
Dr. Novak has his own YouTube channel, lot of info there on anoxic facultative anaerobic bacteria there and in online blogs he has contributed too.
The easiest method to control flow is to install a "T" fitting in-line with the hose powering the air stone.
Off the other port of the "T" fitting, install an inch or two of air line with a control valve connected to it.
When its fully closed, 100% of the air goes to the airstone.
Were you able to increase the temp?
The Ich has started to fall off the fish, and they are either free floating or on the substrate going through its lifecycle like in the video. Soon they will burst and release more.
While they are free floating and on the substrate, that is the only time...
The limiting factor is the angle of the rear door opening.
It may physically fit it back seat, but if the door doesnt open wide enough, then it's a no-go.
How are you going to build the stand ? Or are you getting a pre-made one?
Sounds like a fantastic stocking for a 180g ! !
I've never kept discus, but I do know they like their water very clean. Are you looking at Jack Wattely, Hans, Discus Madness, or another discus vendor ?
Since you have a sump, may I suggest taking some time to research Dr. Novak and his...