Just a couple of things to think about. Ph can drop during cycling so don't be too worried. Also do you know your Kh
? If you have a low Kh
of under 4 there might not be enough buffers in the tank to keep the ph stable. Do a large WC
, wait 24 hours and see if it goes back up. If it doesn't and you think you need a higher ph you can always add some crushed coral to your filter or hang it in a media bag under your filter outflow.