This is what it looks like tightened all the way ( Thanks for the heads up on these fittings Steve - they're great!):
The center "T" accepts a 3/8" JG x 1/2" MPT adapter. The ferts and feed water from the water changer will come in here:
This is what it looks like completely assembled:
How it will work: The water will come in from the left, pass over the pH probe, this way ferts and potentially cold feed water won't contact the probe so directly. Then it will pass though the T where the ferts and feed water come in. The last T is the temp probe. Cold feed water will hit it during the water changes to ensure the heater in the 2128 kicks on.
I'm expecting air to get trapped in the T's from time to time. I intend to deal with it by periodically loosening the "compressor" seals to vent the air out, similar to what is done with some CO2 reactors.
I think it will work well!!!