Hi. I have a pond with about 6 Koi of varying size, I have a submerged pump, an inline UV and a 4 stage Oasis Vortek filter. this used to work fine, but lately a lot of sediment is coming straight through the filter. The vortex works fine when the pump is working at max efficiency, but when the pump gets a bit blocked with weed, the flow drops and it doesn't work so well. The brushes, foams and bio media don't seem to be doing anything. I have replaced the foams, but that didn't help. I suspect I need new bio media, it's sections of corrugated pipe currently. there's quite a lot of choice of media, so any suggestions on that or anything else would be welcome. Thanks in advance.