I have a new tank just setup in the past two days water-wise. I'm using RODI
water as my local water has awful PH and has ammonia in the tap. Water was reconstituted with seachem equilibrium and the two buffers (alkaline and acid). I just turned the filters (an older emperor 280 circa early 2000s) and a brand new fluval C4. Both the filters seem to be "backing up." By this I mean that the emperor has water coming out the front of the intake similar to what it was like when I was younger and would let the filter get too dirty, and the C4 has the red "button" sticking up indicating that the unit needs cleaning.
Both are using new filters (though the emperor's filter was in a storage unit for ~6 years, it was in a box and looked fine when I opened it). Anyone have any thoughts?