CPD death and pH
Just set up a new 36 gallon tank. Have 25 CPDs, 8 pygmy cories, 3 peacock gudgeons, 4 honey gourami. Fishless cycled the tank over the past 3 weeks, have 0 ammonia, nitrite and low nitrate for the past few days.
Have had 3 CPDs die over the course of the past few days. Also have had the pH drop from around 9 (at tap) to around 6.6. This didn't happen during the fishless cycle (went from around 8 to 7.5 in fishless). I do have some driftwood in the tank but introduced that in the beginning before fishless cycle so I don't think the pH drop is due to that.
General hardness and alkalinity are both zero, so the water is really soft. Is there anything I should do to correct this? Would crushed coral in the filter be good? Baking soda?
Tank is moderately planted and I'm hoping to start dosing ferts and excel when they come in the mail in the next few days.