Good to keep trying lot of seedling mix combos until you find one that works well with your environment and watering routine.

Took me two years to settle on this one:

5 parts Black Gold Seedling Mix (basic perlite & peat moss mix), 1 part sifted city compost.

Add soft phosphate, greensand, & crabshell meal into the mix before planting (an Eliot Coleman recommendation). 5 gallons mix, 1 cup phosphate, 1 cup crabshell meal, 3/4 cup greensand.

After the seedlings are 1" high I sprinkle a 5:1 mixture of shifted compost to bloodmeal over the top of the seedlings. This gives them an extra nitrogen boost right when they need it.

Overhead watering is done daily on a timer. Use air pruned cell trays that are off the table.

This achieved about a 80% germination rate, through all 28,000 seeds our CSA planted in trays this year.

After a tray is used, I rinse it out with a hose and put it in direct sunlight to dry. Figure the UV rays will help sterilize it. And I've read the water will activate microbes&bacteria, then quickly drying will kill them.

I don't use coir as it stayed too wet with our daily automatic watering.

Also tried just compost and a 1:1 seedling mix to compost combo, both had poor germination, they stayed too wet.

We grow all of our seedlings in a 4:3:1 mix of coconut coir, sifted worm castings and vermiculite. It took us a few years to get the proportions balanced the way we wanted, but this mix has worked really well for us. This year, we started adding an adapted recipe of the Eliot Coleman fertilizer mix like emgardener mentioned above and it made a huge difference in the health of the plants toward the end of their time in the greenhouse.