Water Ph

[wytch]

hello im new to the forum and fish.   we set up our 200ltr tank and have cycled it for 2 weeks planted it up and left it for a week and then put 6 zebra danos in for 2 weeks and then 3 mollies and a pleco a week ago.  everything is going ok the ammonia is down to 0.25 and everything else is still 0 but i do expect the nitrates and nitrites to make an appearance.
 
any way the ph in my tank is 8.2 which at first i didn't think much of as or tap water is naturally alkaline. last night i was testing the water and the kids wanted to help so gave them some tap water to do the ph of and the tap is 7.2.  now im trying to work out how there is such a difference in the tank to the tap.  
 
we have aquarium gravel from pets at home rinsed and soaked and then added  3 bits of bog wood  one plastic rock thing and plants ( i don't know what they are we just picked them out of the fish shop *blush*)  and java moss.   the danios seem happy  and the mollies are breeding so a doubt the water is causing them a problem just want so ideas as to why the diffarance or if some thing in my tank is causing the problem and i should keep an eye on it. 
 
 
thank you for your advice.

 

[fluttermoth]

First of all, you should test your tap water after ii's been stood for 24 hours. A lot of water companies adjust the pH (to combat pipe erosion), so you need to let that dissipate before you can get a true value.

If it is something in the tank, it's usually substrate, but can be other rocks as well.