Couldn't you use the Fluval 405 to filter if there's no live rock? That would just need sponges, which he may not have thought important enough to mention.
Agreed more flow and if the canister hasn't been cleaned regularly that may help a ton. I did the muratic acid wash on my pukani several times even after curing the rock and it still has an issue with leaching (reason I asked why the kind of rock)This is why I asked. I didn't see anything like that in the contents.
It sounds like the canister should be cleaned more often.
I didn't see an answer to flow in the tank besides the canister?
Using RO/DI should help.
Now I know why you wanted to bleach the rock. If you want to uses the rock again, simply consider recycling the rock in a rubbermaid tub with a pump/powerhead and a heater. Using phosphate media on the tub may be in order if you think the dry rock is loaded with decayed matter. Bleach may work but muratic acid (please research before you use) would probably work best.