I dont think its the ph affecting the gold fish, I ran my system at 8.2 and higher for 6 months before I figured out how to get the ph down. plants actually grew very well but did show a lot of trace mineral deficiency's, never lost a fish, truthfully? only when the power went out on a hot summer day, lost about 50 ready to eat size.
the ammonia is a little high but seems fine for a new ~not yet cycled system, and your nitrite and nitrate levels indicate nature is hard at work.
idealy would want ammonia and nitrite close to 0, and nitrate above 50ppm at all times you are growing plants I try to keep my nitrate off the chart in the darkest shade of red, plants will almost grow before your eyes on a warm day, however this will really mess with tomato, you will see the end of a bloom cluster grow into a stem with leaves, and a stem will even sprout out of the middle of a mature leave, this creates havoc with pruning, training.
I finally used a mixture of nitric, and phosphoric acids to get the ph down over about 4 to 6 days, then I noticed a whole different bacterial bloom, water was cloudy for a few weeks as the tank recycled with a new strain of bacteria, then the ph went down to about 6 on its own before I started adding calcium buffer to keep it at 7. since this forced ph adjustment 2 years ago ph has kept itself low and I have had to keep adding calcium, with the exception of winter when water can drop to the 50's the ph will shoot back up until water warms, at times after a cold winter I have had to help it with a small shot of acid.
my well water ph is 8 to 8.2 year around. and the system as a whole uses 15 to 20 gallons a day, makeup water from evaporation.
in my opinion a different strain of bacteria colonize the tank at a high ph and this strain does little to acidify the water, whereas if you force the ph down with the correct additives to encourage acid loving bacterial growth, they will them become the dominant bio organisms.
do not use pool acid, this is chlorine based and will slow plant growth and kill off the bacterial cultures your trying to promote. never had any luck with sulfuric acid.
others on this list have suggested citric and/or acetic acids.
you have a good bit of learning too do, but very exciting times along the way.