Water Filtration by Reverse Osmosis

What is reverse osmosis filtration? Reverse Osmosis is a method of filtering tap water and purifying it so that you can use it in your aquarium. The water that you get out of your faucet is not clean enough to use in your aquarium and has many contaminants in it. Reverse osmosis basically removes any impurities in the water leaving only pure water (H20) behind. You would be surprised how many harmful impurities are in your drinking water. And while they wont necessary harm you when you drink it, they will definitely cause problems in your saltwater reef tank !

Some of them are very harmful including chlorine and chloramines, and tap water also has dissolved minerals that can cause problems for your corals. One of the best methods for providing the purest form of water in the form of H2O is by using a reverse osmosis filter.

The way reverse osmosis works is that if you hook up your are over filtration kit to your water supply in your house and the pressure from the water supply in your house forces the water through a series of filters. The water pressure from your tap needs to be around 65 psi.

Filters

The first filter, which is a mechanical filter, removes particulates of dirt and dust and other particles by physically capturing them from the water. The water then continues on through a carbon filter. In the carbon filter, it removes all of the chlorine. This is very important because if the chlorine seeps through the carbon filter, it can attack the last filter, which is the reverse osmosis membrane, and actually destroy it. We talk more about that little bit more later on in this article in the second paragraph.

After the water exits the carbon filter that it typically goes into the reverse osmosis membrane chamber. Here the pressure of the water actually forces the water through the membrane and mechanically separates out in the water molecules from the contaminants. A water molecule is typically smaller than most other contaminants, including of many minerals, and because it is pure water, it goes in one direction out of the membrane and the contaminated waste water exits the other direction from the membrane.

Do not use the contaminated waste water for anything in the aquarium. OK, maybe for watering your plants, but certainly cannot use it in the aquarium, because the concentration of contaminants in that water is much higher than even in your tap water.

So the water that comes through the reverse osmosis membrane is then very very close to being pure H2O, around 99.9% pure if you're membrane is functioning properly, and that's very important. You need to make sure your membrane is always functioning properly.

The reason a reverse osmosis membrane works is that the pore sizes in the filter are large enough to allow water molecules through, but small enough to exclude almost all of the contaminants. Remember studying this in ninth grade biology? Many of you have forgotten the semipermeable membrane is a membrane where water pushes up against the membrane under pressure, and the pore size is so small that only pure water comes out the other side is the other side. This is why it's so important to correct pressure coming through your incoming water.

At some point your filters are going to degrade and you need to make sure that you replace them in time, because if you run the filter without each one of the canisters working properly, you could face disaster.Youre going to contaminate your aquarium water with highly polluted water, and cause some very severe problems within your tank. In fact, be sure to read the section on worse mistakes that we've ever made, because the NUMBER ONE mistake on that list is letting your RO filter go bad and polluting your tank with poor quality water!A good insurance policy on an RO systems to avoid having one of your filters not functioning is to put additional carbon filters in line. So your first filter is a mechanical prefilter your second filter is the first carbon filter. The third filter is another separate carbon filter and then your fourth filter is the RO membrane.

The reason we like this setup is if you put a water test outlet (see photo at left) between the two carbon filters, when you sample that water for chlorine, then you'll always know when the chlorine levels getting too high and can damage your RO membrane. This way would chlorine never goes through the last carbon filter, because if it does suddenly get through from your first carbon filter and you detect it you can replace the carbon filters before the chlorine makes it to the ROM membrane.

For the second insurance policy, we recommend adding a second carbon prefilter and making it so that the water that comes through from the mechanical filter and is then filtered by two different carbon filters, not just one.

The reason this is important is because when the first carbon filter runs out the second carbon filter acts as a backup. It's still filtering out the chlorine before it reaches the our own membrane. You want ZERO chlorine making it to the RO membrane.

If you put little T-valve such as a plastic T-valve shown here, between the two you can take a sample and monitor when the first carbon filter is exhausted. You can drop a water sample periodically and test for chlorine. There should be no chlorine in it but if there is chlorine in the sample, that means your first carbon filter has been used up and is no longer effective, and hopefully your second carbon filter hasn't yet been used up.

Its most important that you never allow chlorine to reach your RO membrane.

The problem with this water is as highly contaminated and you can experience a massive algae bloom, primarily because you're fitting and nutrients in the form of nitrates and phosphates and other minerals that would normally be filtered out. And we have found for some reason that even for an hour that a membrane that is not functioning well, it actually gives off more contaminants to the water the regular tap water. I don't understand why this is. For example, in our readings of normal tap water we got about 25 µ siemens, whereas the contaminated water coming through a use of depleted are a membrane was reading 166 !

So that's one good insurance policy. The second insurance policy that we recommend is that you test your water continuously using a conductivity meter.

Conductivity Meters

A Conductivity meter basically measures how much contamination is in the water.

There are two electrodes in a probe which measure the current across the water. And of course the more contamination in the water, the higher the current will be. Your conductivity meter should read about 0.00 on the 2000 scale and 0.00- 0.05 on the 20,000 µ scale.

A great thing about a conductivity meter is it allows you to track continuously how clean your water is. Note that at some point, if it's not as clean as you wish it's time to change the filters.

If you don't have an RO unit, you can purchase the filtered water from your pet store. But if you're serious about the hobby , then I think in the long run, that you need to have an RO unit. They're not that expensive and that way you can rely on the quality you are getting.

if you do have to buy our own water from a pet store is still very important you buy a conductivity meter because a conductivity meter will let you know how pure the water is that you are buying. There's no way of knowing if their filters are functioning properly or not, and even in the best workers in that store can lose track of their new water now and then, and if they have their own conductivity meter you can see them test it.

But you need to test each and every batch before you put your system, whether you buy it from a store, or make your own. But our recommendation is to buy a conductivity meter and preferably by a small RO unit, and test the conductivity of the outgoing water continuously.

And also test the chlorine levels on your RO unit, between the two carbon filters.