Elodea culturing and pH increase

Paul had a very good point about Elodea getting CO2 from
carbonates and causing the pH of the water to go very high.
I use Elodea in several tanks to provide oxygen for my killies
so I was prompted to do several pH tests. To my surprise, the
pH was fairly neutral in the killie tanks. I attribute this to
the peat I have in them for breeding. One container of old green
water, a piece of Elodea, daphnia and no fish had very high pH.
I'd wondered why the daphnia had died in these containers despite
green water and I figure it was the pH. I've added peat to those
containers and 24 hrs later I now test the pH to be about 6.8,
nearly neutral again. Now my question:

Is a combination of peat or soil and carbonates a method of
providing CO2 to plants? Is it going to lead to problems later?

Steve  in Vancouver BC