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Re: What you read
My one experiment with a fish-free plant tank didn't work too well.
I used an aged gravel/peat substrate with a few osmocote pellets pushed
into the substrate around some heavy-feeding plants. No fertilizers were
added to the water column.
Even without fertilizer additions, the nutrients that "leaked" into the
water column either directly from the substrate or through the plants was
sufficient to support nuisance levels of first diatoms, then some BG algae
and later some attached algae.
It didn't take long before I stuck some otocinclus in there. My lowest
fish load in a successful tank is a single SAE in a 20 gallon tank.
Bob Ashcraft wrote:
> OK, lets say I would set up a new tank with a "sterile" substrate, heavily
> planted, no media or sponges in the filter, no fish....just Co2, an
> occasional "shot" of ammonia in the substrate and maybe some trace elements
> when they become depleted for the first couple months.
You will need to have a source for phosphorus in this tank in addition to
> In your opinion, would this procedure have any advantages over adding N and
> P fertilizers to the substrate (as far as algae outbreaks are concerned)
> when cycling a new tank?
Let me see if I understand your question. In the first case you would
have a plant-only tank that is fertilized on a regular basis, using
ammonia added to the substrate as the nitrogen source, and trace elements
added to the water column as needed. In the second case you would add
nitrogen and phosphorus to the substrate at setup (I don't know whether
you would be using ammonia or nitrate), but no additional N-P fertilizing.
The reference to cycling the tank is a little confusing. I'll assume
there are no fish in either tank and that trace elements would be added
to the second tank as needed.
Hmmm. I doubt that it would make much difference; the second case might
be easier. In the first case you could get things just right and add the
ammonia (and P) at the right rate and in the right proportion. In the
second case you might find some time-release fertilizer that provides the
N-P just as needed. Neither case sounds very likely. I think that either
the rate or proportion in which the N and P become available will be wrong
and that a sterile substrate is going to lose either the nitrogen or the
phosphorus or both into the water column. That will feed algae.
I've often wondered how one might keep a planted tank without signficant N
or P in the water column and without extraordinary maintenance. That
would probably mean no fish - or at least no fish feeding. Also, I think
you would need a complex substrate with a high level of biological
There would be a lot of nutrients in the substrate but at any one time the
amount of soluble nutrients would be small - the vast majority of the
nutrients would be contained in biomass and in organic detritus undergoing
slow decomposition. The plants would utilize the soluble nutrients
immediately as they became available, or very shortly thereafter so that
the amount of soluble nutrients in the substrate at any time would never
exceed the ability of the soil to hold the nutrients. If nutrients are
added then they are added in a slowly soluble form (like time-released
fertilizer) or as organic detritus (like compost).
Once the tank reached the plant density that you wanted to maintain your
fertilizer additions should be small and just balance the rate that you
remove the nutrients through pruning or removing plants.
I've never really hit that balance, but I suspect that my nursery tank
with one hungry SAE, a complex and well aged substrate, a "ton" of plants
and fertilizer only as needed comes pretty close.
> Also, would any nitrite spikes be a major concern to the plants?
I don't think nitrites cause a problem for plants at all.