How Is Dontated Media Safe?

[GuppyGoddess]

People talk of being sure not to cross-contaminate when owning more than one tank. How does this differ from having donated media put into your tank? Isn't using donated mature media a risk to a tank it is introduced to, or am I missing something?

Thanks.

 

[Mr Bliss]

Well if there's a disease outbreak in a tank, the filter media will probably have the highest amount of pathogens in it, so it's a realistic concern. But if both tanks are healthy, it's probably no bigger a risk than, say, trading plants between hobbyists.

 

[Tolak]

Quite the opposite actually. Your filter media is a perfect a place for nitrifying bacteria to grow, much better than any other area of your tank. Time for the wayback machine, read number one in post #1 here.

Thanks to biological exclusion, the nitrifying bacteria in mature media crowd out any harmful bacteria.

 

[OldMan47]

I never use media from a sick tank to seed a new tank. The idea of crowding out the "bad" bacteria may be correct but I don't like taking unnecessary chances.

 

[three-fingers]

Why does the idea of crowding out bad bacteria even make sense?

Fish pathogens and bacteria involved the the nitrogen cycle occupy completely different niches...

I think the important thing is that generally the older the tank, the more stable the environment (due in part to biofilm building up, yes) and the less likely small ammonia/nitrite spikes may happen (even between testing), the less stress on the fish, more capable the immune system so less chance of disease.

Also, another potential bonus of older tanks is more DOC's around to complex with metals that come in with water changes, which can possibly harm fish even slightly, stressing them out, less capable immune system etc.

The way I see it, a healthy mature tank full of healthy fish shouldn't have any pathogens in it, or at least, have such a low number of pathogens that the risk from adding mature media is negligible next to the chance of pathogens coming in on new, stressed fish that have come from crowded breeding tanks/ponds abroad, to the lfs tanks to mix with more fish, and then to your tank. Completely negligible IMO.

 

[Mr Bliss]

Yeah, I don't really buy the crowding out theory either. Non-bacterial pathogens like the ich parasite and Saprolegnia spores don't really interact with the biofilm in any way, and can gather in the filter because filters naturally gather stuff. There will also be bacterial passengers on every piece of detritus that accumulates in the filter, and heterotrophic bacteria such as the dreaded Flexibacter columnaris multiply at a rate that's orders of magnitude faster than the growth rate of the nitrifiers. This is one of the main reasons why mechanical pre-filtration is used, because if you get too much organic detritus on the biofilter media, the autotrophic nitrifiers will be completely overwhelmed by heterotrophs.

Anyway, it seems we all agree that filter media from a healthy tank is safe to use, we just have differing opinions on what this safety is based on.

 

[waterdrop]

I'm afraid I have to agree with Mr Bliss and 3fingers here. I don't think think the paragraph labeled "1. Biological Exclusion" by spanishguy111 is correctly applied. I think it is correct that a dominant mature biofilm built up by a particular autotroph, say Nitrosomonas or Nitrospira, means that it has crowed out most of the other similar bacteria seeking to occupy the same niche but that may not have much to do with the life cycle of other types of pathogens. It could, of course, have an indirect effect in that it is altering the water chemistry through its nitrification process, but this is not the same thing as implying that all those other pathogens are seeking space on the media like the autotrophs are. In fact I would expect most other bacterial pathogens to more likely be heterotrophs that would be free to multiply in water (given the right conditions) whether or not there are biofilms on the filter media. And pathogens that are not bacteria would indeed be free to be collected on debris in the filter if part of their life cycle puts them in a position that they are out there on debris rather than on/in the fish etc.

Also, although slightly off-topic, it should be noted for beginners that the image of the biofilms that might be painted by spanishguy111's description (or perhaps many of us from time to time) as being biofilms of nothing but these two beneficial autotrophic bacteria may not be accurate. Its wonderful that Hovanec's three key articles in Applied and Environmental Microbiology raise the likelihood that we've identified the correct dominant species but one set of work in science can't hold complete weight until its been replicated a lot by others and looked at in different ways. It may be that the actual microscopic situations that can arise following the competition for dominance of the biomedia are more varied than our currently accepted knowledge.

WD