Thanks Neil. Actually cut the hole today and didn't go as smoothly as I might have hoped. Bought a cheap hole saw kit on amazon - big mistake. Tried to cut a 4 inch hole and only got 1/4 inch, my Makita drill overheated and the saw got stuck. Eventually tried a different approach, drilled many holes around the partially cut circle, then used a small saw to connect the dots, sort of pumpkin carving but much more labor intensive. Eventually got it done though! Will post pics tomorrow. Also recommend a wet dry vac nearby as there was quite a lot of sawdust, although most stayed in the cabinet or was inhaled by me.
I thought I had a reservoir for the water, but the hole is too small for the pump. Where do you get a 5 gallon clear container with large hole to fit the pump in?
Also put 2 bags CPE and 1 bag Purigen into media rack, interested to see how it affects my nitrate levels. Still left 1 bag of stock carbon in too, had a space for it and figured it couldn't hurt.