Welcome to the forum. Unfortunately this time of year is our busiest time of year and I don't have time to go into a detailed explanation. Cliff notes are you will need to do your research on the DIY system in regards to the CFM of the pump at that depth and how many gpm your diffusers will bring to the surface with that pump. You want to bring between 100% and 250% of the water volume in your pond to the surface every 24 hours once the system is running fully.

If the system is sized correctly, and the start up procedure is followed you will not have a fish kill. You are correct. 15 min day 1, 30 min day 2, etc. etc, until running 24/7. If you smell hydrogen sulfide on any of those days, run it the following day for that previous day's time, and continue to do that daily until you do not smell the hydrogen sulfide any more. Then you can continue to ramp up the run time.

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3/4 to 1 1/4 ac pond LMB, SMB, PS, BG, RES, CC, YP, Bardello BG, (RBT & Blue Tilapia - seasonal).