New Tank Syndrome?

Question
I have a 55 gallon tank with a breeding colony of Tilapia. I male and 5 females. they are aprox 3 yrs old. I inherited them recently ( 1 month ago). I did  transfer them to a new tank but also transfered all their gravel, filter system ( w/ BioWheel) and a large portion (40-50%) of their water.
Since I've had these fish the ph has been low 6-6.5. and ammonia high ( alarmingly green) I have done several partial water changes of 5-10 gallons 1 to 2 times per week. I have added ammo carb to an newly changed filter and aquarium salt. and a whole bottle of Ph up.
I'm a a total beginner but do not want to lose these fish.
I did a large (15 gallon water change) added a 10" air stone and added a water lilly yesterday and had a huge spike in Ph...like totaly royal blue (8-9?) I managed to  get the ph back down to 7 or so but the ammonia levels are still too high...
I'm not sure what other variable you need to know.
I am considering getting a master kit so I can check nitrite and nitrate levels as well.
I appreciate any feedback guidance you may have for me.

Answer
Hi Damon,

Okay, a couple things are going on here.

Everytime you change the water, the gravel must be stirring up.  My guess is the gravel really needs to be cleaned.  Please consider cleaning it and returning it to the tank, spotless and then starting from there.

Also, the ammonia is high because the filter isn't sufficient in some way.

I need more information.  What kind of filter are you using?

Thanks and I look forward to more information in order to help you better.

Renee