Hi,

I am cycling my tank for 3 weeks and I start with one goldfish that I loose in 4 days, than I loose the second one in more 2 days. So I have now the number 3 for 5 days looks like OK now.
I am checking the Ammonia and always is bellow 2. I am doing water changes every day in 20% per change.
Yesterday I made some tests with the PH. (tap water PH6.5, tap water with aqua safe (TETRA) PH 7.0 and Aquarium water PH 7.5). Can I change too much the PH in the water changes? Why the PH is going up inside the aquarium I have just river stones and a plastic ornament.

Thanks.

Have you also been checking your nitrite and nitrate levels? After the ammonia spike a second spike of nitrites happens and this can have more harmful effects on the fish than the ammonia. You should test for it and perform water changes as necessary as it spikes. I'd step up your changes to about 30% too if I were you.
You also need to test for nitrates as they are the good guys and once you get a reading of these it means your cycling is almost done. As soon as your ammonia and nitrite go back to 0 and your nitrates are above 0 then your tank is cycled.