After 10+ years without a planted tank, I am about to jump back in the game with a 400 L tank.
Back then, I worked part time at the local pet-store, and was able to test a lot of reactors. Both internal and in-line reactors.
The best reactor I could find was this little thing from Sera.
It seems like this is not produced anymore. I fint this a bit strange, as it supplied very good surface area between gas and water, making it extremely efficient for its size.
Some months ago discovered a new infill pattern for 3D-printers called gyroid.
I printed a small sample right away to see if it would work within a reactor. The print was a cylinder with 50 mm (2") diameter and a lenght of 100 mm (4").
This has been tested for some weeks at my local pet-store.
It is placed within a siphon tube in a 1200 L (317 gallon) tank with overflow and sump. Water is supplied by a throttled Aquaclear 50.
I did not have high hopes as it came out half the planned lenght due to printer failure, but was really surprised. The pH fell form 7.8 to 6.7 (3 dKH water) in less than half an hour! It was stopped at 6.7 by the pH-controller.
PVC parts has been ordered to test how compact I can make it for my 400 L tank when it is up and running.