just a quick note on test readings, when you give us the results can you give us them in ppm or mg/l (they're the same, just some test kits give readings in one or the other) rather than saying 'safe' or something like that. What's safe for one fish is not always safe for another and it's much more accurate for us to know what you are dealing with if we get actual numbers.
the pH is the least important of all the levels, most fish will happily adapt to a pH a bit higher or lower than their 'ideal' conditions, the danger only really comes in with pH when it's fluctuating, so long as it's holding reasonably stable it shouldn't cause a massive issue.
None of the fish you have are particularly sensitive to a high pH, in fact the guppies are probably loving it! It would be better to lower it a little bit, if you can just work it slowly down to around 7.6 ish then that would be good.
Have you tested for ammonia since adding the mature media from the pond?
The difficulty comes in deciding weather to try to adjust the pH or not at this point. Your priority now is to keep ammonia and nitrite as low as possible, preferably 0 but no higher than 0.25ppm. Ordinarily I would say don't worry over the pH, just focus on ammonia and nitrite for now and worry about the pH when the tank has stabilised and completed it's cycle. However a high pH actually makes ammonia more toxic to the fish, so if you are getting any readings for ammonia you should be trying to get your pH down.
Have you tested the pH of the tap water and rain water that you are using for water changes? If not can you test them and let us know what it is?
There's a link in my sig about pH as well which would be worth a read for you if you've got the time!
