Aquarium Chemistry: Reef Salt Debunked
by Brian Dunat
In the reef hobby, many times it is important to find a routine that works and stick to it. A place where this is common is with the salt mix that people use. Why? Well, once you pick your salt, you generally get a predictable results when you mix a new batch for a water change. Think of this as replenishing the vital elements that our corals and marine animals use like calcium, alkalinity, and magnesium just like the tide and ocean currents would do on a reef in the wild. The question becomes, are you sure the salt mix you are using is the right one for your corals? When you mix up a batch of salt water, are you following a few critical steps?
At Reefnation, we’ve used a certain brand of salt with an orange lid for several years now. We’ve always liked the fact that calcium and magnesium were higher than other brands and alkalinity always fell in around 9-9.5
dkH based on our salinity (.024 – .025). As we stated above, once we got all our dosing pumps dialed in, we were set. We would mix up a fresh batch of saltwater in one of our mixing containers and do our water changes from there. Recently though, in working with one of our LFS partners Sea Escapes, we started to find many of our corals starting to show signs of STN and RTN. Many of the corals polyps were no longer opening up and many of our LPS corals didn’t seem happy. We had just done recent water changes using a new box of salt we had gotten. In doing our water tests, we found that our alkalinity had jumped from around 8.5 – 9.0 dkH all the way up to 10.5 – 11.0 dkH. In general, corals can tolerate about a 1.4 dkH swing in a day without being “harmed”. Anything above that can cause serious damage to corals, especially stony corals.
So what went wrong? In doing some testing, we found that the makeup of the salt had changed. Magnesium and calcium were still right on, but the alkalinity had jumped all the way to 12 – 13 dkH in
a fresh batch of saltwater. So now what? The best thing you can do is st stabilize the system as fast as you can. Even at a less than ideal set of chemical values is typically safer than trying to swing things back to your normal values. Remember the old reef addage “Nothing good ever happened fast in a reef tank”.
Combating Highly Alkaline Salt Water
To deal with this problem, we have slowly decreased the dosing pumps to try introducing the fresh salt water to the aquarium at a slower rate (around .5dkH daily). Unfortunaltely, we have had to frag several of our colonies that were showing signs of STN and RTN to prevent losing the entire colonies. We have also increased our amino and potasium iodide dosage to try and strengthen the corals that are still thriving which has seemed to help as well.
Lessons Learned In Reef Salt Mixing
We’ve talked about the dangers in automating reef keeping in previous articles. Sometimes, we fall into routine habits and stop doing some of the best practices we were accustomed to doing or just plain get lazy. We’re not here to tell you to go find a new salt, rather we’re here to help remind everyone that we need to stay true to our roots and TEST TEST TEST!
One other note that is more of a theory than something we have proven is that not all salt buckets and boxes are created equal. Think about it, if a bucket of salt is shipped on a truck and we know that all the ingredients of that salt are different sizes and shapes, won’t they naturally start to layer over time in the bucket? Maybe by the time the salt gets to your home, the first 2 inches are all bicarbonate ( alkalinity). It would seem at least feasible that if you were to mix up say a small batch of salt using that layer, you would certainly see higher DKH right? In our cases though we are still really scratching our heads. I feel fairly certain that the large brands of sea salt take a fair amount of time to get their mixtures spot on. Then again, are they cutting corners? We use a whole bucket or 2-3 bags of salt for every water change, so we are pretty sure that once our salt is mixed, its a fairly good cross section of whatever the ingredients contain.
Either way, we just wanted to pass this along so that people can share their experiences with similar observations or at least re-establish their regimen of testing EVERYTHING that goes in their tanks!
Have you had a similar experience? If so, please let us know what happened, the impact and how you were able to recover.