SPS will consume a lot but not at the size your frags are at. I would have the test done again or buy your own kits just to be sure.
You want to know:
1. Specific Gravity - if this is low so will your elements (aim for 1.025-1.026)
2. Mg - if this is low your Ca and alk will not rise either
3. Ca
4. Alk
If anything you should consider increasing your water change schedule to weekly versus every 2 weeks. There really isn't a reason for you to run low with a tank your size and the numer/size corals you have. It is possible that your LFS is using Instant Ocean which does run lower on elements. That's not a bad thing but if that is the case and you continue to use their water, you may in fact need to dose. Instant Ocean is not a bad salt mix. Lots of people use it but many times supplementation is required for reef applications. It's really up to you and how much effort you want to put forth. For me, spending a little extra on salt and staying on weekly water changes is a lot easier than dosing. One day I will need to dose but my levels have stayed in range for 3 years without any supplements. Another option is to setup an ATO with kalwasser so that it is dripped in consistently to maintain your levels. This is not that expensive and is fairly hands off.
You want to know:
1. Specific Gravity - if this is low so will your elements (aim for 1.025-1.026)
2. Mg - if this is low your Ca and alk will not rise either
3. Ca
4. Alk
If anything you should consider increasing your water change schedule to weekly versus every 2 weeks. There really isn't a reason for you to run low with a tank your size and the numer/size corals you have. It is possible that your LFS is using Instant Ocean which does run lower on elements. That's not a bad thing but if that is the case and you continue to use their water, you may in fact need to dose. Instant Ocean is not a bad salt mix. Lots of people use it but many times supplementation is required for reef applications. It's really up to you and how much effort you want to put forth. For me, spending a little extra on salt and staying on weekly water changes is a lot easier than dosing. One day I will need to dose but my levels have stayed in range for 3 years without any supplements. Another option is to setup an ATO with kalwasser so that it is dripped in consistently to maintain your levels. This is not that expensive and is fairly hands off.
