fw tank - ph problem - 7.2

[dnsfpl]

no matter what i do, my tank ph will always go back to 7.2

inside the 2x1x1 feet tank
4kg of red gex soil | java moss wall & hc carpet

filter media
100g of peat, wool, 2kg of biohome

fert dosage
flourish 1ml, flourish excel 10ml, per week

did a 25% water change on tues, 30% on wed, using aged water soak with 400g of peat, ph at 5.9

manage to bring down the tank ph to 6.7
but it went up to 7.2 again this morning, before lights on

can anyone rectify my problem?

thanks in advance

http://i38.*******.com/j7gumu.jpg
http://i36.*******.com/nbdfea.jpg

[gman0526]

http://i75.photobucket.com/albums/i303/ReefPR/Facepalm-1.gif

[JeF4y]

Co2..