50 gal w/ Spoiled Guppies , Mollies and 3 Bettas in private tanks
As @Dartmouthseven says , you want 0ppm of ammonia , I also suggest instead of letting the water sit for 3 days that you use a water conditioner that Detoxifies (removes) ammonia , nitrites , nitrates , chlorine , chloramines and heavy metals for all water changes and top offs. I've recently started using the new to market API Aqua Essential , but any water conditioner that detoxifies those things is far better than just letting the water sit. And / or because you said you didn't have a chance to properly complete the nitrogen cycle before adding the fish , I also suggest you use a "good" bacteria starter additive such as Dr. Tim's Aquatics "One and Only" , API Quick Start , Tetra Safe Start Plus. I hope this helps.