Don’t cut him off pellets. You can reduce the amount a bit if you like. Rabbits are different from most other mammals in that they absorb all calcium they eat, then they pee out the excess. A rabbits need for calcium varies of course. Lots of processes in the body are calcium-dependant, for example bone-renewal (constantly going on), dental growth (constantly going on in rabbits) and for muscle contractions. Muscles can’t contract if there’s too little calcium. But before that happens, the body will deplete the skeleton of its calcium content.
In the wild, female rabbits give birth to lots of kits during their life span, and that of course require lots of calcium. This + the constantly growing teeth could be the evolutionary “reason” why rabbits are so good at absorbing calcium.
Cloudy urine isn’t a problem if it happens now and then. Another day your bun might use up the calcium he eats. Rabbit urine should never be colorless and clear. Too little calcium in the diet can cause problems too, especially in house rabbits that get very little sunlight (if the diet is low in calcium, a rabbit needs help from vitamin D to take up all of it. Vitamin D is produced in the skin when the sun shines on it.)
If you’re worried, try to get more water in him. The easiest way is to serve him his veg freshly rinsed and soaking wet. More water means more rinsing of the kidneys.