a very different opinion.


Guru Class Expert
Feb 23, 2006
this is the opposite of what I do, but a well meaning friend who I sometimes buy plants from wrote this today.

"I think you should put some aragonite in your filter and disconnect the CO2. You
need to increase the hardness and provide an alternative carbonate source. Do
that with the lighting you have and you won't believe the difference in plant
growth. CO2 is so misunderstood. It's a substitute for hardness more than
anything else, just a way to provide a carbonate source when it's not available in
the water. It's one of the main reasons I don't participate in any of those
discussion boards. Planted tanks have become techno junkie playthings. I think
most of the people who keep them any more are more into the gadgets than the
plants. Hard water, good lighting and plenty of iron fertiliser are all you need.
I'm getting off the soap box now!"

I somehow can't imagine my tonina's growing this way.. but I figured I'd let Tom chow down ;)

Tom Barr

Staff member
Jan 23, 2005
Sherry, it a way, it's fairly true.............

A non CO2 method works well and the KH is used, the bicarbonates..........

That assumes that the plant can use bicarbonates as a carbon sources, most of the 300+ species or so cannot. Instead, they adapt to low levels of CO2.

Non CO2 tanks quickly remove the KH, then the tanks are well run from then on.
How is that possible?

I agree adding KH is not a bad method for carbon, but it's painly slow and much harder for plants and algae to use.

You can also use KH and CO2 together, but plants will use only the CO2 until it gets very low, then switch to KH, if they have that ability.

So what does that say about preference, growth rates?
CO2 is much better.

The other issue that might be happening, the tank may be Ca or Mg limited and adding aragonite adds more than just KH........
I've used arag in several Rift set ups with plants, I think it does work well.
Look no further to Onyx sand, which is also labelled Grey Coast calcite sand.
Same base materials, different crystal structure(arag vs calicite).

So why wouldn't adding Onyx be better than arag?

Tom Barr


Guru Class Expert
Feb 23, 2006
why would some plants grow best in soft water? why can I grow all the tough toninas with a kh of less than 1? I know they suffer for lack of co2.. when mine went out they grew poorly and the fluviatiilus is only now recovering.

but don't they melt in a high kh tank?

ah or are you saying, that these are among the plants that would not make it in a kh run tank...

I am comfortable with co2 far more so than adding kh.. but it is what I know.


Junior Poster
Apr 15, 2007
Please thank your "well meaning friend" for me. For the heck of it, after reading this post, I added some sodium bicarbonate to my 52 gal low light non co2 discus planted tank. The effect on my Cryptocoryne pontederiifolia was striking. I always found that though growth was consistent the leaves drooped a great deal. Since adding the bicarb the leaves are much more upright.