It sounds like the API low pH test kit, which tests for pH from 6.0 up to 7.6. If it was dark blue, the means your pH is 7.6 or over, which is not necessarily that bad, because it's all relative. I've found out the hard way that you have to do your own research before trusting someone else's opinion. Just because your pH is high doesn't necessarily mean you have to force it to be lower. What you have to do is look at the fish that you have, and figure out which pH range they will happily live in, and what they won't tolerate, and do as little as possible to the water to make them all happy.
As for the filter changes, I am a little unfamiliar with the aquaclear filters. Here's the issue though, if you changed out all the filter media, then you effectively started your cycle over, at least partially. If it has a biological portion that you don't change, like the whisper/tetra filters, then you're OK - those have a bio-cartridge and a separate floss filter with carbon inside, that part you can change whenever you want. But if that's all you have, then when you change it you have to leave the old media in to transfer enough of the bio-colony over, or else you start your cycle over again. It probably has both I'm guessing.
If you started up the tank with filters that came from another system, as long as the filters stayed in water during the move, you should be OK, and your tank wouldn't start over. But the only way to know for sure is to test all levels.
As for the fish, here's what I've come up with:
Silver dollar prefers pH neutral (7) but very adaptable
Bala shark prefers neutral
Plecos are adaptable
So what you might want to do is test your tank water to see where you are in your cycle, test your tap water to see where it's at, do a PWC and test a couple hours later, then 24, then 48. See what effect the PWC has and see what's really going on in your tank.
Then decide on a course of action to maintain a proper (desired) pH level. Usually the best way is to use a non-phosphate buffer to raise the KH level so that the pH will maintain where you need it. Or you can add a piece of coral or a bag of crushed coral into one of the filters, that will naturally lower the pH, even certain driftwood will lower it.