How long should I wait before retesting the ph in my aquarium?

I have a 20 gallon fresh water tank. The ph is testing about 7.6. I added some ph down (by Aquarium Pharmaceuticals). How long does it take to fully permiate the water? I've retested a couple of times but it doesn't seem to be having any effect.It is a new tank, set up four days ago. I just added two small angel fish to help get the bacteria established. Ultimately we want to have two butterfly fish, two more angels, three or four bala sharks and one beta. I'm trying to optimize the water quality before adding other fish.This tank is really just a warm up for the salt water tank I want to get in the future. But I want to make sure I can monitor/control water quality before making that step.

what

it should only take about one or two hours, what fish do you have?

7.6 although a little high should be fine for most fresh water fish.Their is a lot of scare mongering about Ph levels for fish alot put about by shops trying to sell over priced Ph adjusters.Personally I worry about the things that do the harm i.e ammonia and nitrates.I would only worry about Ph if everything else is spot on but you have still got distressed fish.

You should not use chemicals to alter your pH. Its tricky to maintain, expensive, and you could harm your fish from the fluctuation. If you want softer water, I suggest that you buy water that has gone through reverse osmosis, also known as RO water. Usually a good privately owned aquarium shop will sell it for about 25 cents a gallon. You only have a 20 gallon so it would only cost you $5 to fill up your tank, then just a dollar or two when you have to do water changes. You can also add driftwood, that helps bring the pH down naturally.

1 a day

BY THE WAY. IF YOUR ALKALINITY IS HIGH (ALKALNITY IN TERMS OF CARBONATE HARDNESS, NOT THE HIGH END OF THE PH SCALE)THEN YOUR PH WILL NOT DROP UNTIL ALL YOUR BUFFERS(CARBONATES AND BICARBONATES) ARE USED UP BY THE PH DOWN(ACID), THATS WHY THERE IS NO INITIAL CHANGE. WHATEVER YOU DO, DO IT GRADUALLY. REMEMBER, FROM PH8 TO PH 7 IS 100 FOLD (LOGARITHMIC) SO BE CAREFULL WITH THE POTENTIAL HYDROGEN

Your pH levels will vary during the day. It is never a good idea to add any chemicals to your tank. The problem you are having is because your tank is too new and still needs to cycle (develop beneficial bacteria) Don't add any more fish for a few weeks and change as much as 30% of you water with reverse osmosis purified water once a week (it is the only type of water you should use in a marine tank). You could also try temporarily adding some filter material/gravel from an established tank to help out.