Assuming you want to up the flow to help with circulation of CO2 and nutrients, I'd probably get 2 smaller Koralias to distribute the flow more evenly, though with two filters you could just use one large pump. I used a koralia 2 on a 1m long, 180l tank and it worked great. I'd look at getting at least enough flow from the koralia(s) to circulate the tank's volume 10x per hour in addition to the filter; their diffuse flow doesn't blast fish and plants around like the output from a filter or a conventional powerhead so you can use much higher flow rates. I'd get a 4 on it's own or two 2s.