| | Re: How-To: Mineralized Soil Substrate, by Aaron Talbot
It could be the white sand adding hardness to your water. I always had relatively soft water at my old residence and never had issues with the soil raising the hardness substantially.
The ammonia will level out eventually. The yellowish water could be the start of a green water bloom. I've gone through a few of those and they eventually run their course once the tank settles in fully. A few more weeks and it should be well cycled.