So I have been cycling my new 38 Gallon planted tank with the old filter from my cycled tank (aqueon 10) and also a new tetra 40i filter as well as using TSS in the tank The tank has 7 live plants, drift wood, a moss ball, 4 albino cories a golden gourami and 3 neons. My PH for my water has consistently been a 7.4 since the start of my 10 gallon tank. My tap water tests at a 7.4 but strangely the last two days the PH in my 38 gallon tank has been a 6.8 (tested twice each day to make sure nothing was changing the result). I am using the API master test kit. I have been doing 20% water changes daily since I am getting readings of .5 0 5. Any idea why the PH would suddenly drop?