The gritty mix? Add more bark and the effect will be different...

Your question is a bit confusing..I am going to guess that you want to make the 5.1.1 mix based on the following questions..

1 tbsp of lime per gallon is ok...Do not add epsom salts..Add the lime to the mix, not water. No need for epsom salt..

Yes..The Ph rises with the addition of of lime in your very acidic soilless mix.

About the gasses, we'll let the pro's answer this one..

We do know that plants must have oxygen at the root zone in order to maintain normal root function and the soil must be sufficiently porous to allow air to the root system and by-product gasses to escape....

MIke

I limit the organic (bark) component of the gritty mix to 1/3 or less of the o/a volume so there is no chance the organic fraction will decompose and the soil collapse structurally. You don't want the bark breaking up into so many small pieces that they clog the air pores in the soil and create/contribute to the volume of water in the PWT.

We don't usually add lime to the gritty mix - using gypsum instead, and the Epsom salts is added a little at a time to the fertilizer solution each time you fertilize.

Porous soils allow excellent gas exchange in the rhizosphere. They allow gases generated by the composting process (methane, CO2, sulfurous compounds) to quickly escape the soil while air diffuses back into the soil in the other gasses' stead.

Al