Hello,
Firstly, the filter is too small for the cooler, the cooler has a water flow rate of 2000l/h
The cooler will constantly start up. I have made the experience that it is important to have a high water flow, especially in summer. I have replaced my Jbl filter with the SunSun HW-404B aquarium external filter 2000 l/h 4 stages with 9 W UV lamp and filter media. Fits perfectly and the cooler only starts 3 to 4 times a day

I work with a heat exchanger to separate the cooling circuit. I use 13/10 hoses for both circuits and regulate both circuits via a controller with temperature monitoring. Also bear in mind that the cooling unit produces a lot of heat.

Hi :) I had a similar problem with my filter at the time. I then simply took a hose that should go over it quite securely (I don't think I looked that closely, if I measure roughly it's around 18 on the inside and 20 on the outside) and compressed the whole thing directly on the radiator with hose clips. Despite the larger size, I didn't even have to attach any directly to the filter; with a little "pushing" and tightening, it stayed tight despite the larger size. If this doesn't work, a hose connector with the dimensions of the smaller hose could help. You would then need more hose clamps, but these are usually available as a set in DIY stores anyway. ^^