Soft water

[NickAu]

The plants in my 2 foot tank do very well with 1 milliliter of Seachem Flourish comprehensive for the planted aquarium once a week even with low lighting.

 

[StevenF]

An airstone will not change CO2 in a properly set up tank. If at all it will decrease CO2 due to added water movement.

If that is true how does wave and wind action keep CO2 levels in the great lakes at or slightly above air CO2 levels? The fact is that any water will equilibrate with air CO2 concentration for 400ppm. With air at 400ppm it is impossible for a ayirstone to reduce aquarium CO2 levels to below 400ppm.

 

[hobby5]

@StevenF
You are correct that concentration of CO2 in water will equilibrate with air CO2 concentration. For a true equilibrium sufficient water surface movement is needed.

I was referring to the situation in many tanks, where CO2 concentrations are already above the equilibrium concentration (many fish & lots of organics getting degraded by bacteria producing CO2, while only a few or no plants consume CO2), here increased surface water movement would only decrease CO2.

But you are right, in a tank with lots of plants consuming CO2 and only few sources of CO2 production CO2 concentration can be below the equilibrium and increased surface water movement would increase CO2.

Last point: Measurements have shown that normal air stones don't contribute significantly to gas exchange. Important is the water surface agitation.

 

[StevenF]

Last point: Measurements have shown that normal air stones don't contribute significantly to gas exchange. Important is the water surface agitation.

It depends on what measurements were used. For the aquarium hobby KH / PH tables and drop checkers are typically used to estimate CO2 levels but they may not detect the change because they are not directly measuring CO2. To determine if a airstone is contributing to gas exchange you need a CO2 specific test that reads from 0 to 400ppm and O2 levels in the water. These are actually very hard to find and generally not used in the hobby. I have personally observed pearling (oxygen bubbles on plants) are more likely when i have high aeration of the water but seen it is less likely to occur or the plants will produce fewer bubbles. with with less aeration. This tells me increased aeration is helpful.

Important is the water surface agitation.

My last point is that each bubble adds more air water surface area to the tank. So if surface area is important. Adding and air stone should help by increasing the air water surface area.

 

[Myrkk]

I'd just like to thank you all for your help. I've rethunk the tank I had planned and gone for different fish, ones more suited to soft water except my oh bought petricola. .. which I believe prefer harder water.
Intrestingly, since it has matured a little, my pH has risen to 7 but the hardness has only raised 1 to 4.
I did try the crushed coral but no difference was made at all. Also I realised that the advice regarding going with what you have is sound... just took my stubbornness a little while to accept it. Lol.
Busy planning my next tank and my hubby is now trying to pinch the current tank.... he has almost as many fish in it as I do
Thanks for you time and patience