You wanna make sure that you that see alot of cope pods in the tank left. You should have enough live rocks for cope pods to sustain a pair in the 125.
Does the female eat other foods like mysis, live tubeflex, pellets,etc..? What other fish have in the tank? Because fishes like wrasse are a competitor to mandarin in eating cope pods too.
I use have to a pair in a 75 gallon for over 2 years before I down grade my tank. The pair was eating only cope pods and live tubeflex worms. Their stomach are always fat which means they have plenty of food to eat.