Large Filter Systems

[Lenna]

I'm putting this post here mainly because some of the people who frequent this part of the forum have large tanks and know a thing or two about filtering larger systems. I'm asking this question because I'd like to know if the setup in the aquaculture department at uni worries me a little. For example, they have a 1000L tub (2m*1m*50cm) half full, with 2 approximately 785L tubs (1m across and 1m tall) filled with bioballs acting as the filter. There was around 50 3" native grunter fingerlings in this tank. The water is never changed . When I queried this I was told the biological filter would take care of everything and water changes weren't necessary. I'd have thought that this sytem was an incomplete nitrogen cycle since there's not way to export nitrates, not to mention the amount of protein in a system with fast growing native fish. Maybe I'm wrong, but I thought I'd ask.

 

[CFC]

Even perfectly balanced marine set ups with live rock and low livestock numbers need a water change once or twice a year to remove toxins which are not used by the flora and fauna in the tank and replace essential trace elements and minerals that are used up over time. Freshwater and brackish tanks which dont have the benefit of live rock and the nitrate consuming life that dwells in it need far more frequent water changes even in large understocked tanks and no ammount of biological filtration can replace this, there are various nitrate absorbing and converting medias and filters on the market which can lengthen the time that can pass between water changes but they can never replace them completely. The purpose of water changes is not only to keep levels of nitrates down but also to replace calcium buffers in the water which prevent the pH from becoming too acidic and to remove dissolved organic solids from the water column as well as diluting other toxins which may have found their way into the tank such as chemicals from air fresheners, cigarette smoke and general air pollution.

 

[Lenna]

Thanks CFC, I thought it was pretty dodgy. The whole argument started when the fish started to look sick. They dosed the tank with the usual malachite green, which had no effect. They started dying by the dozen and at that point I asked if they'd done a water change. This was when I was told it wasn't necessary. They blamed the deaths on a virus, which they said a water change would have no effect on. Within a week all the fish were dead. I'm really cranky about this because when I try to say anything I'm looked at like I'm out of my mind. I don't think they even have a nitrate test kit! Maybe I'll bring my own in and see if I can get someone to believe me. There's this whole " you don't have an aquaculture degree, what would you know" attitude so I don't know how it'll go.