PH unstable and dropping low

Peat will lower PH, though it will lower it very slowly. This a fishy or a fishless cycle? If you haven't been changing the water, it sounds as if your water comes out with a low buffer, meaning you are experiencing something like OTS. When the tank is up and running, regular water changes will buffer the water, though a little bit of crushed coral will certainly help.
 
crushed coral worked great when i had a tank that would not stay above 6 for some stupid reason, the guide line i was told 1 lb per 15 gallons per point of ph ya need to go above, really i went home tossed a couple handfulls in there and it ballanced out no more ph up swings
 
AquariaCentral.com