These are the only four fish, so there's 3 Pacu and an RTC. As for filtration, it's DIY, there are pics in my gallery. There's a 8x1x3.5 foot area built into the pond which is full of Matala filter media pads, with fine filter floss kind of tucked on the top. PVC runs from one end of the pond to the filter area, over the wall, and then the water runs up, through the media, and over a 3 foot wall, making a water fall. Pumps combined pump about 12,000 gallons per hour. There's also a photo of the freshwater refugium we made for the pond in my gallery. It helps lower nitrates. As for clarity, the filter floss does most of it, but we also add Organica Pond Clarifier every now and then if the water's cloudy at all. It's kind of expensive, but it works really well and you don't have to use much to get the water crystal-clear.