Oxygenation/CO2 Math Question

[Pinkey]

I just got a dissolved oxygen tester. As I suspected, my tanks are highly aerated (25mg/l and 20mg/l). These tanks are aerated with just regular air which suggests the ratio of oxygen to carbon dioxide is approximately 21:0.04 in the tank just like the atmosphere. (20mg/l oxygen : 0.04mg/l carbon dioxide = 25mg/l oxygen : 0.05mg/l carbon dioxide).

Do plants thrive on a lot of available CO2 or a high relative concentration of CO2? I've never looked seriously into CO2 systems. Is 0.05mg/l good?

 

[dougall]

Have you tried comparing your assumed CO2 reading to one based on the ratio between pH and hardness?

If my brain is mathing right this time of day.. .05 ppm of CO2 would be considered kind of low.. if you are considering injecting pressurized CO2 then 30ppm is normally a standard goal

 

[Pinkey]

I have not tried comparing assumed CO2 reading to one based on the ratio between pH and hardness. If 30ppm is a normal goal, that proves that it is the concentration of C02 that that matters. My water is just about super-saturated with air at my altitude and temperature. For the C02 to still be that far below what serious tank planters go for shows me the C02 in aquariums does not occur in nature. That's mostly what I wanted to know. I was curious to know if I happened to have an ideal planted tank situation which would have boosted my confidence to try a few more things. As it is, I have a few plants that grow really well and I'll stick with them.

As a perpetual student, what is the connection between C02 and pH and hardness? My GH is off the charts (significantly above 180) KH is always close to the top (200-240) resulting in my pH being locked at 6.8 without change since I moved into this house nearly 20 years ago. Nitrites, Nitrites, and Ammonia are near 0 which I attribute to the plant/fish ratio.

 

[dougall]

Hardness increases pH. CO2 lowers it .

For example - https://barrreport.com/threads/co2-ph-kh-table.10717/

It's more than a decade old, so maybe assume suggested values aren't necessarily the case now.

But CO2 will come from stuff like fish breathing, decaying organic matter and other stuff.

See also - https://www.2hraquarist.com/blogs/choosing-co2-why/why-inject-co2

And not all plants will take dissolved CO2 as their carbon source. Some will specifically use dissolved carbon, vallisneria for example.

Really . My suggestion if you wanted to try new plants, join an aquarium plant club, and/or make friends and try some for cheap or free.

If you fertilize plants (including mulm or whatever) you will most likely see too low of CO2 in the build up of algae (plant health too maybe, but that can have have more causes)

But seriously check what the CO2 level you actually have is.. I want to say that normal would be about 4ppm, so you seem pretty low.