I have a 150 gallon system and according to the test I used today, there is pretty much no calcium in it. Is this possible? I have only a few small squid in the system, and they are fed shrimp daily. I dont know if it matters, but just in case it does, my system flow includes a large particulate filter followed by biofilters and a protein skimmer, then carbon and 100 micron filters and lastly UV sterilization. I use Instant Ocean made with DI water, and the calcium test showed that was really low too. Is that true? Can this be? is it just a bad test? I have had a problem with animals dying and my other parameters (alkalinity, pH, nitrates, nitrites, ammonia, and salinity) are all normal. any advice?