My pre-filter was clogged so I removed it, and when I did the filter started making a rattling noise as it began moving water again.
I pulled it apart and did a clean - the first one in about 6 weeks. Not sure what was causing the rattle, but it seemed back to normal once I put it back together and turned it on.
What I've been noticing when I take it apart is that the lowest tray, which has 3 sponges, is that there is always a decent amount of sediment on top of the top sponge, the fine sponge. This makes me think that the water is not moving through the sponges and it would have not allowed any sediment to settle there due to the movement of the water.
I feel like the flow of water is taking the path of least resistance by flowing through the pretty significant gaps between the trays and the panels of the filter housing. The filter is a pretty large diameter with a couple of millimeters all the way aorund. It seems that would allow for a pretty decent flow of water. If that is the case, it would be bypassing the trays and straight out the top and back into the tank, and rendering the media largely useless.
The trays themselves feel pretty flimsy and bendy, so you need to be very careful putting the trays back so they line up perfectly. It's very easy for them to sit on top of the other trays wonky and not lined up.
The nitrates are always over 20 despite having heaps of media designed to deal with nitrates and also what I'd say is a pretty heavily planted tank.
Is water bypass a thing or am I just being paranoid??