I'll bump it back up to 100% and try to match what it was at 21 hrs by adjustment to the hang height.In that case at 75% 24/0, you would just need to physically lower the light a little to match the DLI of 100% 21/3. My lights are on these ratchet/rope things, if you have those, you can adjust that to get the DLI you want.
Thanks again!