BTW - Your DIY looks really ugly ;) but also looks like it will work!

I found that really mixing up the kalk a bit longer works better. After it settles and is clear check the PH, should be 12.5 - 12.6 if completely saturated. If not, a bit longer mixing cycle might be needed.

I have used many mixing pumps on my reactor. The paddle wheel type pumps (like a powerhead, but bigger) always fail after a short period of time. Apparently the high PH mixture is just to "Nasty" and the impeller parts break down and fail. That's why I moved to a PW pump.