I only have a couple of plants, and they are most definitely not high end. I was thinking more of whether or not the constant agitation would stress the fish. But i suppose not breathing would be more of a stresser.

I didn't know that about cellular respiration. I was under the assumption that plants gained enough atp from glycolysis, and had no need for the krebs or the etc. Apparently that's mostly single celled organisms.

Looks like somebody has a bit of a background in the biological sciences.

I honestly don't know how much plants rely on respiration. Plants have never been my thang and it's been 20+ years since I've had any cell biology. I only remember the basics, and the only reason I've followed up on it at all was 'cuz I started a coupla planted tanks this time around. Just checked up on it enough to know what I was doing and why I was doing it if I decided to go the high tech route for a planted tank. A friend of mine with a Botany background has a planted tank with CO2 injection and I use him for plant advice. He supported everything I'd read about shutting the CO2 off at night and increasing aereation for that reason. With his background I take it as solid advice. I've got a 55 that I keep bouncing back and forth on: high tech planted tank one day, more cichlids the next day, then high tech plants, then more cichlids, etc. etc. I'd probably have better luck with a greater variety of plants if I set up a high tech tank.

WYite

I'm just starting out my studies, actually. And it really was an only an assumption that plants don't go through the whole shabang -- I mean, how much energy do they need? After further research, I have learned that they need quite a bit, considering they build something from nothing. There are most likely some families with different needs, but otherwise...

Can you keep any fish with your high tech planted tank? Or would the CO2 levels be too high during the day?

I haven't set up a high tech planted tank yet, but generally speaking high tech planted tanks have a minimal number of fish. The planted 55 I've got now is growing cabomba, American val and hornwort like crazy with no CO2 injection and only about 1.5 watts of light per gallon (two 40 watt 6700 k bulbs), with 15 or 20 platies and swordtails in it. Since I'm more of a fish guy and the plants are thriving and providing plenty of cover for the fry, I'm thinkin' about just leavin' it at that.

It is possible to have too high a concentration of CO2. Toxicity occurs when the CO2 concentration in water becomes too high to allow the gills to exchange CO2 from the bloodstream back into the water, i.e. when there is no concentration differential and the CO2 concentration in the water reaches approximate equilibrium with the CO2 concentration in the blood. This occurs around 25 mg/liter or so IIRC, and plants do best at 10-15 mg/liter. I know there are test kits available to measure it. I'd think it would take a lot of CO2 injection to get to 25 mg/liter, but I've never played around with it enough to know if it would be easy to overdose or if overdosing CO2 is something you'd have to work at. I doubt you could overdose with a homemade CO2 injection system, though, so I never worried about it too much.

Seriously, I'm not sure what to think with planted tanks and what the best way to go is. I've tried the Walstad method, with some successes and some failures, and I've tried homemade CO2 injection, and saw a difference in some plants and no difference in others. I've seen tanks that had plants growing like crazy and which were way overstocked. The only consistency in my trials has been too little light will slow/stunt growth and even kill plants. My opinion is what is going to work best depends on what type of tank the individual wants. You won't acheive a Dutch-Style Garden Aquarium with exotic plants unless you have CO2 injection, high lighting and few fish, but from my experience you can have nicely planted tanks with a low tech set-up, hardy plants and quite a few fish. The possibilities are only limited by what the individual wants to achieve.

WYite

My 20g is already starting to look small, so I'll keep the fish as my priority for the moment. This is good info to have for when I get a bigger tank...