Such a thing as too much CO2?

[that guy]

I have had my planted 10gal. tank set up for about 2 1/2 months now using the Walstad method + DIY CO2. Most everything(both plants and fish) has been thriving despite the fact that I only have on 15 watt fluorescent tube for lighting. The only problem I am having is that anything I plant within a 5 inch radius of the airstone for the CO2 just wilts and dies off. The airstone does become covered in blue green algae every couple of days(the only algae in the tank), but I am dilligent about scraping it off. Could it be that CO2 concentrations are too high in this area? Or would it more likely be the toxins put out by the algae, even though it's growth is minimal?


Oh yeah, almost forgot: The CO2 mixture I am using is 3/4 a cup of sugar to 2 tsp of yeast in about 7 cups of water.

[djlen]

Any idea what your CO2 concentrations are? That's a lot of yeast combined in that mixture. I was only using 1/2 tsp. of yeast to 2 cups of sugar in a 2 liter bottle. Seems like with that mixture you're gonna get a lot of CO2 that will run out quickly, cause all that yeast will eat the sugar up. How long does a bottle last you? Where did you get that recipe?
If you know your kH, check it against your pH and see what your CO2ppm is. Just seems like a lot of CO2 for a 10 gal. tank.
Len

[that guy]

Oops, I checked my notes and I've actually been using 1 tsp of yeast. I figured it would be overkill, but I didn't think that would be harmful. The mixture actually lasts a decent amount of time, about 12 days with a steady stream of fine bubbles coming out of the wooden air "stone". I have not checked my water hardness, I will have to do that.

[wetmanNY]

I thought the more usual procedure was, you increased the intensity of the light, then followed with infused carbon dioxide, if CO2 was becoming the limiting factor for plant growth. I can't see how you can get so involved with yeast and soda bottles and diffuser stones without testing for alkalinity.

Cyanobacteria thrives where oxygen levels are low. Oxygen is a metabolic waste product of cyanobacteria, and it hasn't developed anti-oxidants to deal with it...

[carpguy]

The mighty WetMan and his ellipses…

Rarely is punctuation so potently applied.

Plants really like CO2 -- they will not be killed by it, at least not at levels that will leave fish swimming about or at levels that can be generated by a yeast bottle attached to an airstone. On the one hand a little testing never hurts and you really should find out what sort of levels you're getting, and on the other hand thats not the problem.

In good conditions yeast can reproduce rapidly and double the size of the colony overnight, meaning that whether you start with a teaspoon or with two doesn't really make a big difference. The dry form that most of us use contains a large but variable percentage of dead yeast to begin with, so there really isn't any knowing how much you're using.

The Walstad method doesn't include CO2. I'd either follow her advices for a low light tank or not do a low light tank. Tom Barr and the Wetman also have interesting things to say about low light tanks. But raising up one of the legs without the others is bound to give you an unstable tank.