What Size Filter is Right?

What size filter is right? Which size TerminoxISM™ is correct for my well?

The following are three easy steps for determining the correct well water filter for any home. Be very careful about buying anything from anyone who would not require this information before selling you ANY kind of iron filter. It should only take 5 or 10 minutes around the home to get what we need. It is easy to do.

*Visual Inspection In the toilet Storage Tank for Iron Bacteria and Organics.

*How to get a free water test from us, or get a free water test locally.

*How to do a simple flow check to correctly size your filter.

*Please note: If you have an irrigation system that uses well water. You may not be able to do the visual inspections. Because you may not have a working toilet on the water line. In that case, just do a flow rate check and water test only. If you need help, just send us an email and we can have a friendly water quality expert give you a call. Don’t worry, they are not allowed to ask you to buy anything. They just help you figure out what you need.

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Visual Inspection in the storage tank of a toilet

There are two things we look for in the back of the toilet to determine if things will grow in your new well water filter. It only takes about 60 seconds to do. And it is very easy and fun to do. You should do BOTH visuals mentioned here in order to be certain what size filter is right. And what type of filter is correct. If it is a new home and there is no water running to the toilets you can’t do these visual tests. But if you have running water to the toilets, even if it has only been in use for a few days. Do these steps. If you can’t do these two visual inspections for any reason. Just continue on to the next steps, which are testing and flow rate.

How can I tell if I have iron bacteria in my well water?

This is the first of the two visual inspections. Just take the lid off of the storage tank on the back of your toilet. And look on the bottom in the corners, if you can see through the water. But if you can not see through the water. Then flush it to check it. If you have sediment and/or iron and/or dirt or whatever on the bottom of the storage tank. And it is smooth (or settled) across the bottom. That is NOT a sign of bacteria.

But if you have “clumping” in the corners on the bottom of the tank, it is most likely iron bacteria. Any time you see anything clumpy, or slimy, or apparently growing inside that toilet storage tank, you should probably lightly chlorinate the water in our opinion. You can also run your finger along the inside wall of the tank UNDERNEATH the waterline. If it feels slimy or slippery that is a strong sign of bacteria or organics. If it is alive, consider making it dead…. Then filter as necessary. A Terminox will remove the iron bacteria and the chlorine from your household water. So there will be no chlorine in the house or septic normally. And this occurs without any maintenance or carbon to replace. These TerminoxISM™ filters are maintenance free.

NOTE: Never shock the well with chlorine to treat iron bacteria. Over time it will make the problem worse. If anyone suggest that you do so. Stop taking advice from them. They either don’t know what they are doing. Or they are trying to create expensive service call for the future.

Visual Organics Check in the back of your toilet

The visual organics check is done in the storage tank of the toilet to simply determine if things will try to grow in your new filter. If it is determined that things will likely grow int he filter. It is easy and inexpensive to correct. So don’t worry.

Take the lid off of the back of one of your toilet storage tank. With ALL well water, there will be a film on top of the water. It is always there. Even if you can’t see it at first. You may want to get a strong light, such as a good flashlight. And shine it sideways across the top of the water until you see the film. Once you see the film. Lightly touch the water with your index finger. The film will either “repel” from you finger or it will just lay there.

Just tell us what you see. And with few other questions, we can determine if you have an organics issue. But if you have been using any sort of chlorine “puck”. Or other chemicals to disinfect the tank. Or if the water is chlorinated. This test will not work properly. And if you have any iron in your well water. An iron bacteria check would be the correct thing to do as well.

FREE Well Water Testing

We can do your well water testing for FREE if you need us to help you with basic testing. Just send us and email at the email address below and we will send you instructions.

There are several ways to get your water properly tested for basic water problems for FREE! We also have paid testing for the complicated stuff like harmful bacteria and chemicals. Testing is always important when determine what size filter is right.

Private Well Water Testing

If you do not want to send us a sample for free testing. The best thing to do is get your water “independently” tested. Many swimming supply stores do testing for free and are pretty accurate. Just ask them to test it just like they would if you were considering buying a swimming pool or hot tub. DO NOT let the sample sit all day or overnight before testing. pH is a very important part of testing and pH can actually change if it sits too long. Draw the sample and then get it tested as quickly as possible.

When drawing the sample be sure to let the water run until the well pump comes on. So that you are testing the water from the well. And not from the pressure tank. And don’t let the water run through any water softeners or water filters first. You want to test the RAW unfiltered well water.

A great way to get testing is to just look for a local laboratory. Be sure to contact several to compare prices as labs vary greatly in their pricing. You can usually find one that will check your iron, pH, hardness and TDS quite inexpensively. Sometimes for just a few dollars more they will give you a very wide range of tests and we understand what it all means as a rule.

If you have iron issues only

If all you want to do is treat for iron, then hardness and TDS are not always essential to figure out what size filter is right. But it is still a good idea to know theses things anyway. Knowing your pH is always essential. Tell us what is in the water and we will get it right every time. Remember, if you use a lab, pH can change if you let the sample sit for very long. If using a lab, ask them to test the pH right away, even if it takes them a while to test the other things. And remember that we can test for free if you want to send us a sample.

Be careful of in-home salespeople

CAUTION: Never let someone that sells water equipment inside your home test your water as your only water test. They can literally alter the tests by how much water they add to the test tube or apparatus. And they can affect the tests in other ways. They are commissioned sales people. If they don’t sell to you on the initial visit, they make no money. If you are going to buy from an in-home sales person, do NOT buy on the first visit. Then test the water independently of them so that you know what the results really are. Always try to get it tested by someone that does not sell water equipment. Also keep in mind that if you can not find a local lab to help, we can test it free of charge for you. And finally, do not rely on any in-home sales person who does not do a flow rate as described here. Especially the guy that fills a bucket with water and times how long it takes to fill. That is NOT how you do a proper flow rate check for well water filters. We replace hundreds of systems each year where people were sold thousands of dollars worth of equipment, only to have it fail later on because it was not done properly. And those poor folks have already spent the money. Then they have to buy the correct filter..

How to check your flow rate

To figure out perfectly what size filter is right. This third step is the single most important step. Water testing and visuals tell us what needs to be treated. The flow rate tells us what sizes are possible. so the idea is to be sure the sizes match up with what has to be remove from the well water. A flow rate check is pretty simple and easy to do yourself normally. And you should do it yourself so you can trust the flow rate number when you are done. Most plumbers and well drillers have other different flow rates that they look for. That flow rate is usually not a correct number for water filters. If there is a flow rate marked on the pump. That is rarely what is actually happening as a flow. Our simple flow check gets it right every time.

To determine your flow rate please follow these simple steps.

Open the NEAREST faucet or tap AFTER the pressure tank (But NOT the one ON the pressure tank). And let the water run until the well pump turns on. Immediately turn off the tap and count how many seconds the well pump runs from the time it came on, until it shuts off. And then write down the number of seconds the pump ran.

Now get a container you can measure water in. Such as an empty gallon milk container. Open the tap or faucet and fill the container. Then close the tap and dump the water down the drain. Fill the container again, and then pour it out again. Continue doing this and counting each gallon until the pump starts again.

Once the pump starts, shut off the tap and stop drawing water. And write down the number of gallons you counted until the pump started. If there are any partial gallons left over. Count those as well. Such as a total of 1.5 gallons, or 4.25 gallons. You now have the information to calculate the well pump flow rate. Once you have the number of seconds the pump rant on the first step. And the number of gallons on the second step. . Just let us know what it is. And then we can tell you for maximum flow rate.

For example: The well pump ran for 30 seconds. And then you were able to draw 5.5 gallons before the pumps started again. That means you have 11 GPM flow rate.

Things to remember when doing a flow rate check:

*DO NOT use a water hose when checking flow rates. If necessary have someone listen for the pump to turn on while you draw water.

*If you can’t hear the pump turn on and off, follow these instructions. When you have a pressure tank. Somewhere near it there will be a small box with some wires connected into it. This is called the pressure switch. Right when the well pump comes on it will make a distinctive “Click”. When the well pump goes off it will make another distinctive click. In this case you may need two people. One to draw water and the other to listen for the clicks.

*Variable Speed Well Pumps and Constant Pressure Well Pumps:

Most residential wells have conventional pumps and pressure tanks. Every now and then we will talk to someone who has a different type. These people usually know who they are because of the special nature of these pumps. If you have a variable speed pump or a constant pressure pump, please contact us.


We can help you size the right system. Including every other kind of filters or softeners that you can imagine. We can refer you to reputable water filter companies where you can buy all of our products. And where you can buy other products that we recommend Just send us an email and tell us what you are trying to do. We can even have a professional water analyst call you if you would like to email us your phone number.

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Just click on a link below for more information about TerminoxISM™ Iron, Sulfur and Manganese well water filtration systems. Terminox Reviews

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What Size Filter is Right?