Hi Isaac and welcome to the forum
Aiken has covered it pretty well, as usual
The pH of the water can affect how the ammonia affects the fish. If the pH is below 7.0 the ammonia is less toxic to fish compared to if the pH is above 7.0. Having said that, nitrite (the next stage of the filter cycling process) is less toxic in water with a pH above 7.0.
Your pH of 7.5 is fine for goldfish and whilst the ammonia will be a little more toxic in the water due to the pH, do not worry about the pH. As long as it stays around 7.5 it is fine for the fish.
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You can feed the fish once every couple of days. They should eat the food within 20-30 seconds. They won't starve and will be fine getting fed a couple of times a week. Unlike birds and mammals that use most of the food they eat to keep warm, most fish take their body temperature from the surrounding water. This means any food they eat is used for growth and movement. This allows fish to go for weeks or even months with little or no food. Once the filter has established, then you can feed them more often.
The filter bacteria take time to grow (around 4-6 weeks but sometimes longer). During this time you minimise feeding and do big regular water changes to keep ammonia and nitrite levels low. In a couple of weeks time you should start to get a nitrite reading. A few days after that the ammonia levels should drop to 0ppm. A few weeks later and the nitrite levels will go up and come back down to 0ppm. When it does the filter should be cycled.
Don't bother testing for nitrates until the tank has finished cycling because nitrate test kits read nitrite as nitrate, and give you a false reading.
Make sure any new water is free of chlorine/ chloramine before you add it to the tank.
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You can contact your water supply company and ask them what the
GH (general hardness) and
KH (carbonate hardness) of the water is, as well as if they use chlorine or chloramine. You can also check their website for this information and water company's usually have a page showing what is in the water.
Most water conditioners have a single dose rate for chlorine and a double dose rate for chloramine. Check the instructions on the dechlorinator.
At this stage, just reduce feeding, do water changes, don't add any more fish until after the filter has established, and wait.