Question about Petkit Eversweet drinking fountain, 1.35l

Hello, with two cats the fountain is empty in about 5 days.

I replace the water at the same time as I refill it.

The water is perfectly filtered.

I clean the fountain about once a week.
I only rinse the filter with water and the other things with Pinol sprayer as this is a natural product and therefore the animal does not come into contact with chemicals and it also has a disinfectant effect.
The filter should be replaced every 2-3 months. I notice this as soon as the water no longer flows downwards through the filter fast enough

With our 2 cats, we changed the water every 2-3 days (we waited until the fountain was almost empty).