Our Aquarium is an 125 Gallon Acryllic Tank. Using a Sump system.
We installed a Coralife Turbo-Twist 6x 18 Watt UV Sterilizer from Oceanic Systems, http://www.oceanicsystems.com/products/turbo-twist-uv-sterilizers.php. It is large enough to support a 250 Gallon Aquarium, but I've always been told to purchase something larger then required, for either growth/future support or because the size smaller was rated exactly at size. This one item removed a slight green color from the water right after installation. It was installed on the down spout from the Aquarium feeding the sump. But, I need to move it to after the filtration so it doesn't have to deal with the unfiltered water.
We installed an AquaticLife 60" 4-Lamp T5 HO Light Fixture, http://www.aquaticlife.com/t5ho/index.html. I am still attempting to set the timer correctly. The colors are amazing, hasn't impacted the temperature of the tank.
I purchased a RENA Filstar XP4 http://www.planetrena.com/Rena-XP-Filstar-Filters.html. Again the one larger then the recommended size. Our current Sump setup appeared to be working correctly, but the kids were complaining about the water stinking. It definately had an undesirable odor, and our current filtration setup was slowly dying so we needed to come up with something better. The instructions state it can support the distance we have for water return using its builtin pump, so I installed it without our current sump pump for return with the hopes I won't need it. I have the sump pump for return, and plenty of hose in case it is necessary.
After installation of the RENA Filstar everything appears to be working fine, although the return jets are more like gentle hoses. We were given a Hydor Koralia 4 Circulation Pump http://www.hydor.com/prodotti/show/famprod/27/list/12. So I installed it to give the tank a little more turbalence on the water surface for Aeration. The fish just started swimming face first into the pump.