To co2 or not to co2

Actually, you'll always have a limiting factor for plant growth. In many tanks, CO2 is the limiting factor. Once it's bumped up, then light or ferts limits the plants. So, you begin a game of adding better lights, then fertilizing, then bumping the CO2...you get the picture.

So, rather than just saying yes or no--I would decide how much maintenance you want to do, what kind of lights you'll have, etc. Keep in mind that the success of the smaller planted tank won't mirror to the larger tank. The increased depth, different stocking, ect will change the success of the plants.

Originally posted by ArkyLady
PH 6.8 and KH 3 works out to about 15ppm of co2, which from what info I've found is the optimal co2 level. Am I right in assuming for a moderately planted tank with moderate lighting (2 watts per gallon) that I shouldn't need to add any co2 to have a successful planted tank?

Click to expand...

This does not address your original question, but if you are not injecting Co2 (they way I am reading it) then I would bet one of your tests is off. You should not have 15ppm on aged water without injection. If you tested right after a water change or from the tap, it is possible, but it will not stay that way.

The loss of co2 is caused by the surface aggitation the bubble wand causes. The balance between O2 and CO2 in water will be the same as in the air when you aggitate the surface and thus allow for the free exchange of gas between the water and the air.

Co2 is added to a tank in order to facilitate lush growth and/or to be able to grow plants that wont thrive in a tank without it. I run tanks from 1 wpg to just over 3wpg but only add co2 to the 3wpg tank. I have a couple of tanks at 2wpg that get great growth without co2.

What I can tell you is if you run co2 on a smaller planted tank, make sure you have a good sharp scissors

co2

Here is some very good information on co2 and aquarium chemestry.
http://www.csd.net/~cgadd/aqua/art_plant_co2chart.htm
I agree that it would be very odd to have 15ppm co2 stable in an aquarium, even more so when running an air stone which tends to cause co2 to come out of solution that much faster. The co2 usually runs naturally around 2 to 5 ppm I think, unless adding co2 from a tank, yeast, etc.

I also have a kh 0f less than 1 and a gh of 3. Out of the tap my ph is 6.4. After it ages it jumps up to 8.0. I had to inject CO2 in order to keep the pH down.

On the other hand, my water is great for shellies.

Generally not.

Your KH should stay pretty stable, testing pH with a reasonably accurate narrow range kit will give a good indication.

But if you plan a non CO2 tank in the first place, soft/hard etc matters not for the plants. They do well in either after a month or two.

They will use up all the CO2 in your soft water the same as they will in hard water. Hard water will have more total Carbon =more KH, HCO3 which some plants can use, albiet at a slower rate than CO2, soft water will have less carbon as KH. I'll be specific here that I am talking about alkalinity(KH generally=> HCO3-) here, not general hardness(GH=> Ca++ and Mg++).

The CO2 present in soft or hard water in a glass let setting on a table will be the same. The hard water will have a pH of say about 8 and a KH of 20 and the soft water will have a pH of 6.4 and a KH of 0.5. Both waters have the same CO2 level, 5.9ppm in the case I used here.

It's the _plants_ that will remove the CO2(the acid) for their growth. This is not equilibrium now. The plants will change this. Your pH will move when you add the plants since they will remove the CO2.

The the pH will go up when the plants do this in either tank. The starting point of soft or hard really doesn't matter. Both tanks will be depleted equally of the CO2 once the plants start photosynthesizing. One will be left with more carbon as KH, (HCO3-), the other will not.

You need some KH to buffer the acid when you add CO2 gas to keep the pH level stable and easy to test for. 3KH is good.

This CO2 is what plants like and will be quickly used up when you add much light ....around 1.5 to 2.0w/gal. Soft or hard water. The same plants in softwater or hard water added to the water at equilbrium will use about the amount of CO2. If you add CO2 you still need to add the same amount in either tank. The plants need the same amount of CO2 and both soft or hard water tanks will get depleted at higher light and the plants will

Anyway, the plants will soften the water pretty good after a while of simply topping off the tank for evaporation if you use the non CO2 approach.
You are not adding CO2 in the non CO2 approach so don't bother with testing for it. If you do add it and want better plant growth, then you will test for it.
Many are very content with non CO2 tanks if they follow some general guidelines.

If you use the CO2 approach then the water change methods come into play.

I see you cannot "afford" CO2 but can afford a 150 gallon planted tank. Okay This is NOT a question of you being able to afford it or not.

You can do it this way but if you want better plant growth etc, want to do lots of water changes etc, you will run into some trouble likely without going to CO2.

Faster growth is not the goal with CO2 generally, better healthier growth, less algae is. If you keep the 2w/gal lighting level, then adding CO2 will have a profound effect on the plants without causing weekly trimmings etc. Folkks can also use slow growing plants etc to reduce any "work".Some folks like the "work".

But I'll work with folks either way they decide on, there's a great deal of CO2 myths and a fair amount of pro CO2 bias on most boards.

A nice trade off is using CO2 with less light, 1.5 to 2.0w/gal is ideal to use with CO2. This reduces dosing, algae, growth but still very healthy, provides some wiggle room if you neglect something, cost less, and you still get most any tank design or layout and plant choice you want.

Weekly water changes and once a week dosing usually takes care of most issues.
Try CO2 on the small tank and see if you like it.
Stick with using the CaCO3 to keep the GH/Kh up.
Onyx will last for awhile but will mellow with age IME.

You can see some very nice examples of nice plants growing in hardwater systems both in Florida, SEA and in Brazil. Softer waters often have fewer plants IME and plants very close to the surface.

Regards,
Tom Barr