Please provide full list and set up of your tank
Size of tank(in litres)?
Are you filtering the water ?
Are you dosing any liquid co2?
What lights are you using?
Do you have any livestock in the tank yet?
You have an nutrient rich substrate and you are also dosing the water column I'm going to make a few assumptions
There are plants that do not require high co2
You are not dosing liquid co2
There is also NO livestock in the tank.
You do have a filter on the tank
Please change 50% of you water daily for the 1st week then every other day for the 2nd week.
If you are that bothered about the fluctuating co2, please perform the water changes an hour before your lights are due to turn on.(I really don't think it will make a huge difference)
As mentioned I'm making some assumptions on this post
It would be worth on a low maintainence tank to get yourself some liquid co2 and also ensure you have good uniform flow from your filter.
Or some algae loving fish
(I prefer no to dose co2 and have loads of algae in my low tech tanks for the ottos to eat)
Sorry for any typos