Great advice but phosphates actually can be zero... technically. If your algae and tank are eating it as it enters, you’re feeding them a healthy meal. So technically even though it’s being introduced, it’s being eaten before it can be detected.
I consider the water from my 3 LFS stores to be good but I have never tested for phosphates or nitrates. I'll have to do that next time. If Saullman does this it could rule out, or in, your concern
One way to control nitrate and phosphates is to use it. I think I remember you said you had a skimmer. That is important with carbon dosing. You have to be careful because it can drive those levels to zero, which is not healthy either. So, you have to test for nitrates every other day per instructions. This won't help a lot until you can pin point where the nutrients are coming from and correct that too. I've used it and it works.
In a reef tank, stability is above anything else, most important. By switching water from other LFS, you are throwing pH, salinity, Ca, Mg, and other elements off. It’s a major shock to your system. Most likely they use different salts. They most likely don’t use RODI. I highly recommend anyone who is serious about a long term reef tank to make their own water.
