pH Issues

OK, I finished fishless cycling a 15 gallon for my four year old son tank last week. Story of that is elsewhere here, but it was ultimately successful after 5 weeks.

So, yesterday, my son and I went to a LFS to get some fish. He really wanted Glofish (those transgenic zebra danios), so that's what we got...two of them to start with.

Anyway, the pH in my tank is 7.8, it stayed that way through the whole fishless cycle. kH is 120ppm, or about 7 dH. Now, I'd read here and elsewhere NOT to mess with pH. The owner of the LFS, however, was absolutely adamant that I had to lower mine, he keeps his tanks at 6.5 and I confirmed this with my own test. So, I got some Ph decreaser and lowered mine to about 6.6. I spent about 1.5 hours acclimating the two danios to the new tank (mixing 1/4 cup of tank water with the bag water and removing more and more LFS water). Fish went in the tank and all seemed OK.

I didn't realize, until I started reading more stuff today, that my water has pretty decent buffering capacity and that ph decreasers wouldn't keep it down long...lo and behold, when I came home from work, the pH in the tank was right back up to 7.8. OK, I'm NOT going to mess with it anymore! That's where it wants to be, apparently.

So, two questions:

1) how much damage did I, stupidly, do to these poor little danios by having the pH go from 6.6 to 7.8 in about 24 hours? They look great right now, very active and all over the tank. What should I look for in terms of problems from this pH swing?

2) are zebra danios OK in a pH of 7.8? I take it they'd ideally like it somewhat lower, but I know many fish can be tolerant of variation. Are they one of them? I get different answers about the right pH for them everywhere I look.

3) In the future, can I buy fish from that store? They are the only one that carries the GloFish that my son wants. I'd ignore is Ph lowering advice, but can I really successfully acclimate fish to such a big difference (6.5 to 7.8)? Or, should I find a store that keeps a higher pH and just convince the little guy to settle for whatever they carry?

Thanks for the help!! I was patient enough and withstood the LFS misinformation enough to complete my fishless cycle properly and after all that work, messed up right from the get go .

accidental dupe, can't figure out how to delete.

Thanks! Hopefully these guys will be OK. If we go back for more GloFish, would a slow drip acclimatization be enough account for to account for the pH difference? Or, do I just give up and find other fish at another store...one in my actual town (this guy is two towns over) might have the same weird (soft, but high Ph) water that I've get from the water department.

I was also a bit annoyed because he refused to sell me more than 2...I understand that they like to be in schools of at least five. No matter how many times I explained to him that I'd done a fishless cycle and that the tank has been successfully removing 2ppm of ammonia every day for at least a week, he told me I couldn't have more because I'd have ammonia problems. There is no way that five little danios make 2ppm of ammonia. I guess it's just as well, or more fish would have potentially been hurt the the pH swing.