# Fish load in a Walstad type planted tank?



## Baysin (Nov 12, 2010)

I'm a fairly experienced aquarist, but totally new to aquatic plants. I've been lurking about for a bit while gathering my funds, equipment, and wits to start my first planted tank. I've done a lot of research and feel generally confident in what I'm doing, but there's one thing I've not seen much information on, and that's the amount of fish load you can expect to keep in a "low tech", natural, Walstad method tank. It seems that, while there may be plenty of oxygen available to fish during the day since the plants should be generating it, at night you'd expect to see a gradual drop in DO without some sort of aeration, as both the fish and the plants are using oxygen for respiration. We don't want to aerate the water since this will eliminate our limited supply of CO2 for the plants. Will the DO levels drop to dangerous levels for fish? Do you have to therefore keep fewer fish than if you were using conventional filtration and aeration? And if so, has anybody tried any methods of injecting O2? Is that even a good idea? Or maybe just flipping the lights on for a few hours during the middle of the night to replenish the O2 reserves, like a sort of anti-siesta? Or am I completely off base here?


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## Jark (Feb 6, 2010)

You want some water movement in the tank to get aeration. You just don't want fast or ripply water that will gass out too much CO2. It doesn't take much water movement to get O2 in the water. If you have a filter or powerhead in the tank just adjust it so it causes light water movement at the surface without creating waves. Don't worry about lights at night. It will through the plants cycles off and stress the fish.


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## mthom211 (Sep 3, 2010)

If your worried you could put an air pump on a timer to turn it on when the lights go off and off when the lights go on.


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## Michael (Jul 20, 2010)

Moderate water movement as Jark describes is plenty for gas exchange at night. All though Walstad recommends moderate stocking levels, many El Natural owners find that the tanks can support full conventional stocking levels easily because the plants do such a good job of keeping water quality high.


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## davemonkey (Mar 29, 2008)

Baysin, I think it all depends on how densely planted the tank is and how established/mature the plants are. 

In my daughters 10gal NPT, she had 10 fish at first when the plants were young and barely growing. In the mornings at "lights-on" the fish were sometimes gasping for a few minutes. Now that the tank is mature and the plants are super-dense, she has at least double the recommended stocking rate (there are 20+ fish (not on purpose...long story), and each is at least 1.5 inches or more) and there is never a gasping problem. Her lights are on for about 12-14 hrs a day, depending on when she gets up and goes to bed, 30 watts t-8, no siesta, no filter/aeration of any kind.


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## geeks_15 (Dec 9, 2006)

My daughter also has a 10 gallon NPT with no filter and no water movement. The tank is planted moderately and holds about 6 inches of fish (4 harlequin rasbora and a pair of young apisto cacatuoides). The tank is about 2 months old. No problems. No fish loss or evidence of distress. No nitrates, nitrites, or ammonia on tests.


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## Baysin (Nov 12, 2010)

Cool, thanks for the replies all. I figured, no matter what, it'd probably be best to start with fewer fish and work my way up as the plant growth takes off. Heck, that's what I'd do if it wasn't planted anyway.

I intend to be testing my CO2 and DO levels once I get going, just for my own education, so I'll be able to keep an eye on that and experiment some, but I wanted to get a sense of what I could expect to accomplish, fish wise. I'm keen to try a planted tank, but the point, for me, is to have an interesting fish tank, not an interesting plant tank that happens to have some fish in it, so keeping the amount of animals I'm accustomed to is something that matters to me.

Good info on the powerhead, by the way. I was intending to use one just to circulate water anyway, but I wasn't sure if it'd be okay to have it stirring the surface a little or if it really needed to be kept well below the surface.

Thanks again for the replies. Now if the holidays would just get over with so I could have time to get this stuff set up!


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## Diana K (Dec 20, 2007)

Gas (oxygen and carbon dioxide) enter the water where the air and water meet, but the gases do not move through the water very much. This is why fish hang at the surface when oxygen is getting low. The top fraction of an inch is higher in oxygen. 

For plants and fish to thrive throughout the aquarium the gas exchange at the surface needs to be mixed with the rest of the water. A small powerhead or filter that creates some water movement with gentle ripples at the surface seems to be optimum in most tanks. This water movement also circulates fertilizers and gases that are generated deep in the tank such as from decomposing waste.


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