The carbonates being absorbed isn't a huge deal, as long as you don't allow the pH to crash drastically. As long as kH is 1-2 you will be fine. My kH out of tap is only 1, and I've never had any issues. When I first started with the sts, I simply added some baking soda for the first 3-4 water changes. Since then, it's been completely fine. The sts has a very high cec, so this behavior is expected. It's not all bad, either, because these minerals will be kept for the root systems in the substrate. Don't be afraid to use sts because of this. The fact this occurs makes the substrate VERY good.
Thanks for the info. My Kh from tap is about 3dkh and the tank is about 2 so I should be ok. Ph is stable now at about 6.4. I just need to get some fresh baking soda.
It's not that I'm afraid of using the STS it's more I'm avoiding the time & work involved in changing it. LOL I've got to find several consecutive hours which has been hard here lately. Plus I've been waiting for my new driftwood to stay sunk so I can remove some of the rocks that's holding it down.
Now that the weather cooled a bit I'll try harder to get it done. That way the fish can stay outside in containers rather than having to find room in my house. I can use an outdoor extension cord to run my HOB &/or sponge filters in the tub(s). Then I won't have to worry about being in a hurry. I have a tendency to keep messing around with the plant arrangement so it seems to take me forever to get it just right.
I've got a low-tech, lowish light tank. I only use Excel, Comprehensive and Sulfate of Potash and some root tabs around my Sword. Don't really need NO3 in this tank as it's never below 30ppm. I could take my remaining root tabs & put them in there and add some Sulfate of Potash. How much of either would I use for 40lbs ??? Should I break up or crush the tabs? Sorry for so many questions but appreciate the help.