Hello If i had some oyster shells i would put them in a sack and pulverize them ,the smaller the size of the particles the more readily uptake happens.
I buy the powered oyster shells myself.
I am of the opinion that 80% of ones base mix should be 65-70% Ca & 10-15% Mg.
If you get close to this 80% of your base mix being of this ratio your pH will be right where you want it 6.2-6.4
I also think that if there is a way for you to recycle your mix that you should to get the microbe-life working for you.
Adding back in a complete fertilizer or in your case Calcium and a magnesium after every grow.
I also add back all the leaves and stems from the previous grow ,after all these contain every thing that the plant wanted.
I also believe that being a good grower in using true living organic techniques that you must know that ultimately the plant is the conductor in deciding what it wants by what exudes it sends to the roots.
I build my pots with buried treasures of a complete fertilizer that feature low ratios of things trying not to go over anything that has higher ratios then a 8 IE; 3-8-8 bulb food or 0-3-0 soft rock phosphate a teaspoon or 3-4 on the bottom of your pots going into flower will give the roots the choice over mixing them in globally.
I also opine that liquids bypass the microbes which in turn retards their growth.
I mean if someone brought you a TV dinner every time your hungry would you bother working for a hamburger?
I also do a wet dry kind of cycle in using TLO techniques For I never let the medium dry out COMPLETELY.
Here is how I do it ,I look at a pot as having 3 layers a top a middle and the bottom.
I'll let the top go completely dry the middle will be going from moist to dry with the bottoms just going from wet to moist.
I know this from using a probe showing these dry-moist -wet levels.
I also water every time with a tea design to bring in more microbe life and see this new influx of bacteria eating the carcass of the life that died from the dry down.
In time you will discover what works for your growing techniques and you will think of it as your style.
Now we all need some style!