A few species can spawn and have viable eggs in an alkaline pH, but these are the exceptions. To obtain an appropriate neutral pH, use peat filtration, blackwater tonics, or pH Down. Add ph Down carefully. Hardness and pH meters are a must if you are playing with water chemistry. Meters give you greater accuracy than test strips, and the results are instantaneous.
Soft water can be touchy at low pH ranges, so be careful.
The need for good filtration cannot be stressed enough. Low pH and soft water bring about low bacteria counts, especially if you have no gravel. This may seem like overkill for a pair of apistos in 15 gallons of water, but the best water quality possible is the goal. Undergravel or box filters can trap fry. I use a gravel washing siphon to remove the water and clean the gravel all at once.