Adding biofilter to recently established pond

[jmilana]

Hi pond people. I have a new (two months) little pond (~150 gallons) with seven 4-6" goldies. There are a couple of water hyacinth and a few other plants, all doing well. The fish are fat and happy, active, eating well, and it looks like they're starting to spawn. The water is about 65 degrees, a little cloudy but tests good (a little hard, a little high alkaline, but acceptable), but I've been treating it with AlgaeFix every three or four days and it's slowly resolving. I had a 40W UV sterilizer from the big pond, but the bulb broke and I can't afford a new one. The problem is that the nitrites are way high. Nitrates are fine. I've done partial water changes and added salt and Stress Zyme, but it's still too high, although the fish seem unaffected. I'm just running a little Laguna PowerJet 400 pump through a waterfall, cleaning out the Laguna once a week, with no bio filter. I wondered if I can install an old Hozelock Cyprio filter I used with my former 1200 gallon pond. It's been unused for over a year, but I filled a tub with about 25 gallons of cycled pond water and have been running it through the Hozelock all day. Can I just go ahead and install the Hozelock now between the pump and the waterfall or should I wait some specific period of time? Is the Hozelock safe for the fish, given its year of inactivity? It was really healthy when it was filtering the big pond, but is the presumably dead bacteria (if any) remaining in the filters harmful? Any help would be greatly appreciated, because I'm really concerned about these persistent nitrites. Thanks!