Eh…so so for the meter…they , honestly, show wear and tear fastest…clean the tips for accuracy…it is a start!!!
When you get comfortable with pH, you will test your water, not the soil. Water you use pH(with and without nutes), water in the tray at the bottom, the run off pH. Good times!!
So, Digital pH meter on Amazon
These types are better, really aim for this kind, please
25C-26C is better for babies, 30C getting high, 31C is high…the babies just don’t grow well
Condensation on the domes means good, high humidity…if nearby, open them to air once in awhile…
Looking great, sorry for the critical, but imo honest, opinion
you should aim for a pH of 6.5 in a soil grow, ±.3…so 6.2-6.8 is best, 6.5 the “sweetspot”
The fan only helps a spindly, tall plant, at this stage…your plants are a good height…and better light helps a tall, spindly plant more, anyways.
More to read 
A note about digital pH glass globe electrode probes