Plant impacts on fish capacity

DKRST

How significantly do plants impact the fish capacity of a tank?
I'm curious because most everything I have read from other hobbyists here seems to indicate that plants increase the capacity of a tank to house fish (I'm referring to biocapacity, not "swimming room"). Opinions?

Assuming a single species tank, an adequate filter, proper water changes, and good tank maintenance, what are your thoughts on how many more fish a heavily planted tank could house above the "typical" capacity of the filter/tank without plants? 0%-200% ? Somewhere in between? This is more for a discussion, not a definitive answer since tank stocking depends on so many factors!

Geomancer

Good, no definitive answer, I can do that =)

I'll just say one of the variables is how fast the plants grow, the faster they grow, the faster they assimilate the nutrients (ie Ammonia, Nitrite, Nitrate).

So a tank full of Anubias and Java Fern isn't going to do as much as a tank full of stem plants and floating plants.

So no idea on the percentage, I imagine you'd have to slowly add fish, and checking how quickly Nitrates rise to determine a balance.

Byron

I agree with Geomancer but only up to the last sentence. Nitrate is not the only issue, as I'll try to explain.

In non-planted tanks, nitrates are a significant indicator of water quality, but only with respect to the nitrification cycle. In natural (low-tech) planted tanks the nitrates should be very low because of the plants' rapid assimilation of ammonia/ammonium primarily, and perhaps nitrite and nitrate. But with the plants grabbing much of the ammonia/ammonium, little goes through the nitrification oxidation to end up as nitrates. And there are bacteria that take up the nitrates. This occurs in non-planted tanks too, but here the nitrifying bacteria are on their own to oxidize ammonia to nitrite to nitrate. So, all else being equal, nitrate would be somewhat higher in non-planted tanks than in planted.

But the "crud" that you cannot see or measure in any manner, is the real issue. Pheromones released by fish that other fish can "read," dissolved waste and urine, and I don't know what all else--this is the stuff that filters can't remove and for which we use plants and do water changes. In planted tanks, the more plants there are, the more of this "crud" they can take up and remove. Which is why we can get away with fewer water changes, or less volume, with live plants. And again, this crud cannot be measured.

So that brings us back to DKRST's initial question. And I agree as I said that faster growing plants will remove this quicker. But of course, there is a limit to the capacity of plants in a closed system. Some time back I read that a 55g heavily-planted tank that was stocked with 6-7 Neon Tetra would be self-sufficient with respect to this issue, and never require a water change. The plants would handle the "crud" with this minimal a fish load. And no filter either, just the plants doing the job naturally. Diana Walstad, who advocates no water changes, says this works with well planted tanks with what she calls "a small or moderate number of fish." I have considerably more fish than what anyone could call small or moderate stocking, hence I do weekly 50% water changes. But I have no actual data as to how far I could let this go by simply relying on the plants.

Byron.

DKRST

Nice response Byron, thanks!
Assuming everything else being equal, I'm the hypothesizing that a high-tech tank with pressurized CO2 and medium-high light should have a greater "processing" capacity for fish waste. That set-up could would work well with an overstocked tank since water change % in a high-tech tank are often greater than 50% per week.

AbbeysDad

The thread opens an interesting conundrum. The 'crud' Byron speaks of is essentially dissolved organics...the aquatic equivalent of compost tea in my organic garden. Fearing it's bad in the planted tank, the water change will remove much of this (organic fertilizer) to be 'replaced' with chemical ferts... hmm.

It would seem that a moderate to heavily planted tank could offer an additional buffer for an increased bio-load, however one can't discount other measures that make it equally possible. Regardless, we can never let our guard down in providing the best water chemistry we can for our finned friends.

AD

Byron

A correction here...my term "crud" is for the partially "unknown" pollutants along with those we do know are present--pheromones, urine, liquified waste, plant chemicals. All these pollutants cannot be measured, and they are not dissolved organics. In nature these are so widely dispersed that the fish do not remain in them for more than a few seconds. Water changes will remove these, and plants will take up some of it but with our normal stocking levels no where near all of it.

Mikaila31

Plants consume quite a bit of bioload. More then a lot of people expect. But as already mentioned it depends a lot on their growth rate. I've maintained filterless tanks with moderate stocking levels without any problems. Before I moved it and it started to have issues, the 15gallon supported 24 Neon Tetra sized fish,many shrimps and snails for many months. Its water quality was actually the best out of all my tanks at the time. Most my planted tanks have decent or heavy stocking. My 20 recently had really really high stocking levels for a couple weeks. It was over 2 fish per gallon lol. The tank and fish didn't seem to mind in the slightest.

One thing I think is over looked is plants prefer ammonia. They will take ammonia before nitrates. But taking the ammonia means the nitrates are not even produced in the end. This is why I prefer to go with minimal filtration and more circulation in planted tanks. Use a smaller filter then normal then just add a powerhead to make flow. Heavy filtered planted tanks the plants and filter are competing for the ammonia. What the filter gets will end up as nitrates. What the plants get is removed from the system.

Byron

I think we're on the same page Mikaila, but one thing you didn't mention that I wanted to check, namely water changes. If memory serves from from your other posts, you do weekly water changes?

Byron.

Mikaila31

Since I moved last June... I'm not terribly sure . I no longer have a specific day of the week to do water changes. I've also gone from perviously having tap water with 20ppm of nitrates to tap water with 0 nitrates. I'm pretty sure I currently do 50% water changes every 1-2 weeks on most my tanks. My one soil-filterless tank I haven't touched in a long time, but its been basically plant/shrimp only for a while. Its been doing lots of weird stuff lately and I just don't want to deal with it -_-

DKRST

I'll attest to ammonia's impact on plant growth. My Myriophyllum never grew so well as the time I had a filter clog and my ammonia level crept up unexpectedly! Grew more during that week than than it does with CO2 now! Obviously, ammonia isn't necessarily something we want in our tanks, but if I had a plant-only tank, I'd be tempted to try fertilizing with (very) small amounts of ammonia to see what would happen!