Pond filter arrangement

no1catman

Have forty-five goldfish between 4" to 10" - have been told I have too many for the size of the pond. An air pump has been added, which will help with oxygenation. It was recommended I change the (revolution) filter for a bigger one. Given that I'm also told that the pump is if anything too powerful (but the wattage can be adjusted). Doesn't seem logical replacing a filter that works, just to get a bigger one, wouldn't it be better to get an additional medium filter and run them in sequence - that is using one pump. Or, would it be better, to spend the extra to have filter + pump - better flow over the cascade, and if any pump problem - at least one still going.
Any thoughts, advice.  .