I have been running my 29 gallon with 12 fancy guppies for nearly 4 or 5 months. I want to know if it is safe to introduce 10 guppies at once?

i am relatively new to breeding and have never crossbred before. i crossbred a plain blue female guppy with an endlers guppy i got at petsmart last week. will it be a big endlers guppy or a tiny blue fancy guppy? or is it just chance?

Can someone tell me what meds I can add to my aquarium to help one of my fancy goldfishes. He has this huge tear in his tale. Its all red. This happened maybe in 1 or 2 days. He is in there with another fancy goldfish. They have been in my 25 gallon freshwater tank for about 3 years together and...