[Xiangliang2]

Raising KH in an aqua soil tank is generally something you don't want to do. The soil itself is designed to keep a low to zero KH. I see adding carbonates to a soil tank like adding a humidifier to a room you've installed a dehumidifier in. Aqua soils have a finite lifespan that is accelerated by how much carbonates they have to absorb, which is why most of us using it use RO water with only GH boosted. Add to that, the bacteria you are trying to colonize adapt to water parameters just like fish do. It's my understanding that you want to culture these in the water parameters the tank will ultimately have, as @Econde said. Probably no harm in what you've done, but I would let the soil do its job and drop it back down. You can only rush cycling a tank so much and by changing the parameters and then changing them back, it's probably only serving to make your cycle take longer.

https://www.plantedtank.net/forums/...s-cycling-buffering-substrate-0kh-low-ph.html
https://www.plantedtank.net/forums/29-substrate/1208378-can-fluval-stratum-stall-fishless-cycle.html

Searches on this forum have discussed using tap water (which raises KH) to start the colony of bacteria, and then switching to remineralized distilled water when the colony has been established. I understand your concerns about expending the buffering capacity of the substrate, however other hobbyists have claimed the period of time spent cycling won't expend the capacity. If you have had a different experience regarding this please let me know.

My original question was not concerned with whether or not my buffering capacity would be reduced. I am asking about whether or not I should be adjusting my CO2 input due to the change in my drop checker.

 

[Xiangliang2]

Your tank water and dc water are in two isolated chambers and should not contact each other. Changing the tank’s KH should not affect the dc KH. Your situation makes me think that ether the CO2 levels are varying or the tank water is leaching into the dc. Is it possible that your CO2 has changed due to a change in surface agitation or for the hours after a water change?

As a double-check on your dc readings, try using the 1-point pH drop method, but be careful to ensure that the dKH reading is the same in the tank as it is in the sample water. When doing this it also helps to increase the accuracy of your dKH and pH readings. For dKH (assuming an API-type test), use 25ml tank water and divide the results by 5. For pH, a pen is much better than a reagent kit.

If you can run the 1-point drop test with this better accuracy, I would use that as my guide to adjusting CO2 and pushing higher than 1-point is fine with the permission of your fish. Use the dc just for general monitoring once you set your CO2.

Thank you for the response, you reasoning makes sense. For some reason today the color change happened later than it usually did, and it coincided with me adding the KH so I assumed the two may have been related. I did a top off today so perhaps the CO2 gassed off instead of building up for the color change at the usual time.

 

[Xiangliang2]

Not sure why you are running CO2 while cycling, I assume you are worried about your plants?

In any case if you want it to cycle faster add a bottle of Dr. Tim's, Tetra SafeStart Bacteria or Seachem Stability.
For Bacteria growth you don't need a lot of light(3 hours at 50% is more than enough per day), CO2(low or preferably none), water changes(don't do unless you have Ammonia >2ppm) or fussing in general let the bacteria do its thing in the dark.

The plants will be fine for a week with low supply of these things. Please don't try to add Carbonates, manipulate pH, or do anything other than let things develop in a normal environment(CO2 not necessary) for 3 days you can shut off CO2 it should be fine.

Also for monitoring pH better to use API kit or a ph probe DCs are innacurate and always delayed readings from the measuring the tank water directly.

The issue has already been resolved. I am running CO2 because I am carpeting E. parvula, which doesn't do well in the conditions you mentioned, especially not during the cycling phase where ammonia is high. Lowering light and CO2 sounds like a recipe for algae takeover since it can propagate much faster than E. parvula. My concern is not with pH monitoring, rather the unexpected change in my drop checker. However, I realized that the drop checker change was an unrelated coincidence.

I have experience in cycling, this is not my first tank. The context of me raising KH is based on other hobbyists' experiences in cycling a tank with buffering substrate and CO2. I have linked their discussions in my previous post.