Ooo! I forgot about that. But wouldn't it dissolve at some point into the water inside the plant, lowering its pH and forming carbonic acid? Same effect as what I'm playing with, but works regardless of tank pH.
All biological critters and weeds use CO2[aq], even us, our lungs still have to go from CO2 [gas] to a CO2[aq] in our blood.
The insides of cells are not gas, they are liquid water.
You are simply reducing KH this way, I think RO would be a better solution than Acid for most folks. Certainly much safer, less toxic, smelly, less prone to the many risk involved with a strong acid at a high concentration.
Folks can also easily kill all their fish if not careful.
This is asking for trouble.
In theory, you can lower the KH, and yes, CO2 is given off, just like vinegar and baking soda. But how much CO2 is given off and is that really what is causing the results you see occurring?
I think the relative amount of CO2 is very small.
I think it's far more likely the issue is you are now simply comparing softer KH to harder KH.
You also have a CO2 management issue in the first place.
Plants may or may not pearl, but this does not imply they are not growing etc well or not, even so, if you have fish gasping, you have other issues, not related so much to CO2, but of O2/circulation and light intensity.
Fish respiration is a function of BOTH CO2 and O2 concentration across the gill/ More O2, the more/higher the CO2 concetration can be. If the O2 is low, then even a little CO2 addition will send fish gasping to the surface.
I often suggest good current for the fish health and well being, most all advice does. Plant aquarist sometimes reduce the flow to save their CO2, bad idea.
Some start off with excellent flow when their tanks are hardly planted and they are waiting for it to fill in. By then, 2-6 months later, the weed choked tank has virtually no flow comparatively. While plant O2 production can counter act this some, often it does not.
So more flow and surface movement is required to keep up, or more pruning, or you can also use less light which will reduce the demand for CO2.
So less in that case is better as far as management of CO2.
More light= more demand for CO2.
So you can manage this several ways, RO, peat, strong acids, reduced light intensity/duration, better flow/current, surface movement etc.
Given the trade offs and fish health, I'd not use strong acids.
Okay to add a few mls to a trace water mix of CMS+B etc, but not much else really.
It was a discovery for me, but not new in the hobby. Wllbldrco recently posted that chart and the other info on which I based this experiment. As long as the pH is low enough to shift the balance to carbonic acid, the plants benefit. Most people do that by using RO/DI water, whether they understand the reasons behind it or not. I simply substituted a different method for reducing pH. If I had RO/DI water, I'd use it instead.
I think if you want more CO2 for the plants, then add more CO2, it's much simpler than what you are thinking it is.
If all we had to do was reduce the KH, and then CO2 would be a snap, everyone would have long done this. It's fairly well known that at low KH's, a number of species do well and most plants do better overall as long as we add CO2 gas.
However, this has nothing to do with adding HCL and releasing CO2 for the plants that way.
The amount of CO2 released and the time is stays in solution is brief.
And if you add too much HCL and there's no KH left after, then you really knock the pH way down and kill your fish since now there's no buffer to address this strong acid. Something like a weak acid will not harm fish in most cases in this case, but a strong acid will. Good luck with that.
I see burns, bad lung/nasal issues from fumes, spills, splatters, corroded spots all over the house, angry spouses, dead fish, still not addressing the root issues, many better alternatives.
Use RO if you want lower pH/KH.
Or use CO2 better and stop gassing your fish, keep the O2 up, use less light so there's less issues with CO2 demand.
My tanks use low light, pearl and no gasping fish:
Plenty of examples over long time frames.
Here's my tank from Santa Barbara tap water with a KH of 11 and Gh of 24:
Pearling is strong, there's also a lot of current.
Work on the real issue; CO2/O2, do not avoid it.
Fish will be better off and far less risk.
Your self also