LFS told me not to do a water change on my new setup for 60-90 days. I have a new 150 gallon tank and am new to the hobby. My nitrates are at 20 consistently with a red sea kit. LFS measures them at 0-5. I have two fish in the tank, scarlet cleaner shrimp, and fire shrimp. Also my cleanup crew is small as of now, with 3 starfish, and a mix of snails totaling 24. Only four of which are turbo snails. Is this no water changes for a while idea good advice? If so, should I be worrying about the nitrate levels???