Originally Posted by Grah the great
Hi everyone! I understand that many aquatic plants can use carbonates as a substitute to CO2...so, in a low tech tank that was already hard and alkaline, would plants benefit if small amounts of baking soda (NaCO3, or Sodium bicarbonate) were dosed daily? I was thinking of dosing 1/8th to 1/4th a teaspoon per five gallons over the course of the week, which would add 3.25-6.53 ppm carbonate a day. If done in small doses every day, this shouldn't change the KH rapidly enough to harm livestock. Thanks :-)
To state that kh/bicarbonates are a fertilizer like co2 is, is inaccurate at best. However, if you have absolutely no carbon in your tank (zero kh and zero co2), your plants won't grow. Please read all of my edits below.
I dont know if I i can find proof that this wont work, but what I'll say is that kh (and therefore carbonates) in no way make plants grow as fast as co2.
If that were the case simply having a kh above 0 would help them grow fast.
Edit: I'm reading the chapter on Carbon in Walstad's "Ecology of the planted aquarium" now. At first, it seems to be fundamental that co2 is what plants need, and bicarbonate and carbonates are not it. You can lower the ph to turn the bicarbonates into co2, where 8.5 ph is half co2 and half bicarbonates.
However, the next page talks about how seaweed etc in saltwater grows much faster than the fastest growing freshwater plant. The hypothesis is that seawater plants have adapted to leverage the massive amounts of bicarbonates (salt) in sea water.
So from what I can gather, the only way bicarbonates can substitute for co2 in freshwater plants is if the specific plant can do it.
Again, if this was normal then we wouldnt be dosing co2 into our tanks and kh would be magic.
Edit 2: I've attached a table from the book so that you can see just how low photosynthesis becomes when the plants are limited to bicarbonates instead of co2. DIC = all forms of carbon in the water, total.
Assuming other factors are nearly the same, it's a difference of 5.33x when comparing 10 am (co2 @ 76%) to 2 pm (co2 @ 2%).
Edit 3: Ah, there is a complete section on co2 vs bicarbonate uptake. Essentially, even the hardest water plants (meaning they expect kh/bicarbonates in the water) grow at least twice as fast when given appropriate amounts of co2.
In general, it says freshwater plants prefer co2 to bicarbonates 10 to 1, possibly because bicarbonate use takes up more energy. Freshwater plants leverage bicarbonates less effectively than even algae.
As a final note, some plants have gone as far to avoid using bicarbonates directly by making the immediate area a lower ph (around 6) so that the bicarbonate reacts with calcium in the water to form co2 for the leaves to absorb. Obviously in this case, co2 would be more efficient for the plants. A plant that does this is Potamogeton lucens.