which one is the sediment filter , mines been running 50/50 for six months but now its 75/25 in favour of waste . how do you know if its not the resin and when its time to change the resin , water pressure about 70 tds about 120 any info cheers

your top one is the sediment filter - you will notice a drop in flow when you need to change , just like you have now .
resin change - TOP tip i found with the merlin is not to run it through a DI at the same time when you have the merlin on .
As the merlins pumps out fast i was finding i was eating up resin and changing/ renewing every month as it dosnt get time to do it's thing .
What I now do is run the merlin straight into a 1000 IBC tank - then pump it into the van tank , then I let the van pump the water through the DI and then through the hose and out the brush.
I have been doing it this way now for 7 months and still on the same resin !!! the slower flow from the van pump gives the water more time to pure itself .