Agree, do NOT spend money on a ph meter.
You've done very, very well getting them this size. I envy your success with them!
Your fertilizer plan is reasonable enough, in my mind. But if those run out, I'd switch to one that is a 3-1-2 ratio. I cannot say that the acid part of Miracid is hurting or neutral or helping them.
One problem may arise and that is, fertilizers are salts in chemical terms and your watering in small amounts may well be leaving salts to build up in the soil. Maybe you should stop the fertilizer for a while.
I cannot offer more advice. I have been trying to grow and winter over a geranium or two for 2 or 3 years with very frustrating failures.
