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Re: Filterless plant tanks
On Sat, 20 Feb 1999, James Purchase wrote:
> But aren't you missing the benefit of mechanical filtration - even without a
> heavy fish load and possible overfeeding, plants do produce detritus. Do you
> just leave it in the tank to decay?
Detritus is mostly the product of the fish and fish feeding. I see very
little recognizable plant debris in my unfiltered tanks. Partly because
Snails remove the dead plant material about as quickly as it appears.
And yes it's left in the tank until it's removed by the occasional
vaccuuming. Only one of my unfiltered planted tanks ever has visible
debris. I think it shows up there mostly because the surface of the
substrate in that tank is very fine grained and the debris can't just
settle in.
> Not all filter units are noisy.
Absolutely true. But even some quiet filters produce enough of a hum when
they operate that their absence when turned off is noticable.
> And a
> mechanical filter will not remove any nutrients from your tank (it might
> remove some nutrient precusor products).
I've never seen an analysis of the solids from a planted aquarium. I have
seen some information on the solids produced in aquacultural operations
and I suspect that normal aquarium solids are similar. The solids are
very nutrient-rich and for regulatory purposes can be regarded as manure.
Data from an aquaculture site at Purdue (I think it was) sites studies
showing the solids contain 10% to 30% nitrogen and 1.2% to 3.5% phosphorus
(dry weight basis). Certainly the remaining material will be a rich source
of calories for detritivores as well as minor and trace nutrients for your
plants.
If you're feeding a "steady state" fish population, then all of the
nutrient content of the food ends up in the water, and (again based on
aquacultural data) at least 40% of that is going to be either uneaten or
passed by the fish. That's quite a bit of nutrient content.
If your filter removes solids then the nutrients in the solids will be
removed with the solids. The amount that's removed will be highly
variable. If you have an efficient mechanical filter that you clean
frequently, then you may strip a lot of nutrients out of the tank. If you
have a poor mechanical filter (or perhaps just a sump where solids
collect) then rather few solids will be removed. Your filter isn't doing
anything. If you have a mechanical filter that you don't clean frequently
then a lot of those solids will be broken down between cleanings and the
contained nutrients released back into the water; again, your filter isn't
doing much.
I'm not sure there is a useful distinction here between nutrients and
nutrient precursors. Detritivores and bacterial action can convert a
substantial amount of the nutrients contained in the solids to
plant-available nutrients in rather little time.
>
> What do you use to provide water circulation in your filterless tanks?
Some filterless tank keepers use no circulation. I use powerheads as
circulating pumps in most of the tanks. One tank has an aquaclear pump
without media and the last tank has a submersible pump in a small sump.
All but the aquaclear are completely silent. The aquaclear makes some
noise and I'll probably replace it some day. None of the pumps have a
prefilter finer than the intake screen; in two tanks I've constructed
intake manifolds to spread the inflowing water out over a larger area and
reduce the intake velocity.
Roger Miller