No need to panic. Most large breed wethers don't have to live long...so the breeders don't worry about UC.
What happens in an normal, intact male goat is his urethra widens as his testicles mature. If you wether early, this widening doesn't get to take place and they will have a narrower urethra.
UC (urinary calculi) is when the phosporus and calcium ratio is off in the goat and the urine forms crystals. In a narrow urethra, this spells disaster...whereas the longer you wait to wether, the more margin for error you have.
Ammonium chloride is an acidifier. You can order it through caprine supplies and also get it from vets (we get ours from our vet). Sometimes it is in tablet form. You just powder it and add it to the diet. Some feeds also contain AC - such as Purina Show Goat. The acidifier helps to break up the crystals or prevent them altogether.
The biggest things to avoid are sweet feeds and overfeeding (fat goats). With careful prevention, you should be fine.
We lost a 4 month old buckling (not even wethered) to UC when we were just getting started with goats. We were feeding sweet goat feed at the time with alfalfa hay and the Ca/Ph levels were way off. Even with huge doses of AC and a pizzle trim, we were unable to save him...so we're scared to death of UC now and do all we can to avoid seeing it again.