Welcome to AA!
The Aqueon 55 supports 325 GPH
(Gallons per hour), and the emperor 400 gives 400 GPH
giving you a total of 725 Gph
. Since you have goldies (They are more messier than other fish) you could add another source of filtration.
That is your choice if you want to add a canister and keep the HOBs on or off, or Getting another HOB
filter to add the GPH
If you do decide to replace the HOB
filters with a single canister filter, Make sure to keep the HOB
filters on with the canister until it can collect enough beneficial bacteria so that the HOB
filters can come off. (I recommend the EHIEM classic series)