Gavanizing vs Chlorine


With the latest stock tank pool craze, there are literally hundreds upon hundreds of articles, pictures and how-tos on everything from installing and levelling the tank, deck building around the tank and how to install the pump, fittings and hoses. Even we have an article about what makes a good stock tank that you can see here. Most of these articles do NOT talk about some of the very serious safety issues that need to be taken into consideration when installing a stock tank and modifying it for a pool of some sort. We will be covering those issues in another article found here.

With that said, there are however extremely few resources available that discuss chemicals and other substances that hot-dip galvanized steel should NOT be used with, or at least where caution should be used if galvanized steel will be used in a specific application. In this article, we are not even going to try to list all of the chemicals that are corrosive to galvanized steel, we will only discuss a few chemicals like chlorine, bromine and salt that are specific to swimming pool environments that concern the galvanized steels rate of corrosion.

Since the use of hot-dip galvanized steel immersed within pool water is NOT a typical or recommended application, let’s start by discussing what uses these tanks are actually recommended for. Our galvanized stock tanks are meant to be put outside and filled with untreated pond, river or well water, this is the “official recommendation” for these tanks. (this is why we recommend using our poly tanks for your DIY backyard swimming pool.) The very small amount of the zinc coating that is absorbed by the water is actually good for animal health and the natural antibacterial properties of the zinc help keep the water in the tank cleaner and fresher longer than in poly or plastic tanks. Their massive size and strength make them a no brainer to use in watering livestock like cattle and horses. Generally, galvanized steel performs well in solutions with a pH between 5 and 12 (natural untreated water), but other factors such as aeration, agitation, ion levels, and temperature also affect its corrosion rate. For example, soft water with low levels of magnesium and/or calcium ions and has high oxygen or carbon dioxide level can be extremely corrosive to galvanized steel. On the other hand, hard water that has a high level of magnesium and/or calcium ions will develop protective scales on the galvanized coating that will act as a barrier to corrosive substances and can greatly extend the service life of galvanized steel in the water. 

Even though regular untreated water that is too hard or too soft affects the galvanized coating, it is at a MUCH, MUCH slower rate than treated water and a good quality coating will usually last years and years. 

Even though you have read our recommended use for these tanks you may still want to have one because of any number of reasons other than and including their absolute beautiful, rustic look. If this is you then here are a few things to expect. The coating IS NOT DANGEROUS! Here is the WHIMIS sheet for galvanized coating.  The FDA recomends XX of zinc in your diet, the small amount absorbed by the water is fine. When treating the water, absolute care must be taken. With high levels of chlorine in the water, a very high rate of corrosion might be expected for hot-dip galvanized steel inside the tank below the water line (see Fig 1). The expected lifetime or corrosion rate for hot-dip galvanized products in pool water cannot ever be exactly predicted, as the chlorine level, temperature and water hardness of the pool will fluctuate over time.  However, the coating can be expected to perform anywhere from a few months to a few years unless a barrier coating is applied to the submersed areas.

FIG 1. shows a new tank that had a bag of pool shock put in the water for 1 week.

When it comes time to clean the tank many people will turn to bleach or vinager, DON’T DO IT! Bleach, even when mixed with water, is VERY corrosive to galvanized steel and vinager is use to actually remove the zinc coating from the metal. An alternative cleaning solution is a mixture of one part ammonia with 10 parts water and then rinsing the galvanized coating with fresh water and allowing it to thoroughly dry. However, standard dish soap with warm water and a brush is the best solution for most clean up of normal organic dirt and buildup.

Since we are Canada’s largest supplyer of these tanks we took it upon ourselves to see if we could find any solutions to help with these problems. We teamed up with CreKote and put together a wipe on clear top coat that can be applied to your NEW or undamaged inside surface. This coating will create a barrier beween the chlorine in the water and the zinc coating greatly increasing the service life of the coating. You can find this coating on our website here.

If you have already purchased a galvanized tank and over did it a bit with the chlorine and have damaged the surface inside we are looking into solutions that can be applied to help stop the corrosion and smooth the inside surface out a bit to make your taink as good as new again.

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