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How to Lower Ph in Your Tropical Fish Tank

by | Mar 18, 2019 | 4 comments

Our Secret Ph Hack


Welcome back to the Jack Wattley Discuss hatchery, I’m Gabe Posada. Today we’re going to talk about a little PH hack and how you can get the right levels in your tank. A lot of people have told us that the water coming out of their tap has a PH of between 8.4 and 8.9. Now, this level is okay for coy fish, but you can’t keep Discus or Altums properly with these levels.

What can I possibly do to fix this, you might ask? Well, it’s actually very simple. We came across a little hack roughly 20-25 years ago, and we have been using it to get the proper PH in our tanks ever since. We use a common household chemical called muriatic acid, which can be found at any Home Depot in the pool supply section, online, or any other pool supply stores. You can also use phosphoric acid, however; the more readily available one is going to be muriatic acid.


What You Will Need


The first thing you will need is going to be some muriatic acid, which can be found at any hardware store with a pool supply section. Typically, they sell by the gallon and depending on where you live you can probably pick this up for around four dollars.

Next, you are going need a regular 35-gallon garbage pail to mix the treatment in. Here’s a little tip, don’t try to be slick and buy one with wheels so you can wheel it around. Remember each gallon weighs seven pounds, and once you fill the garbage pail it will weigh upwards of 300 pounds. Those wheels can’t handle that much weight, and it’s going to end up tilting over and messing up your floor if you try this.

To make the process easier on you, and so you don’t have to manually scoop up water and put it in your tank with buckets, we recommend you get a little utility pump. You can get them online, or at any hardware store, and will probably not be too far from where you find the muriatic acid. They are plastic, fully submersible and usually come with a garden hose adaptor.

Lastly, we use a custom-made adaptor to make filling the tank easier. All you will need to make it is some PVC pipe, plumbers waterproof glue, and a ball valve. They say a picture speaks a thousand words, so check out what we are talking about below.



How To Lower Ph In Your Tropical Fish Tank Jack Wattley Discus


 Making and Testing the Mixture


First, you fill up the garbage pail with roughly 35 gallons of water. Once the water is in, you can now grab the gallon of muriatic acid. We use the cap of the gallon container as the measuring device for determining how much to put in. Everyone will have a different baseline Ph balance in their water, but we always start with two caps full worth or muriatic acid to start with.

After adding the two caps full of acid to the water, you’re going to leave that water alone for three days. During this period, the chemical reaction between the acid and the alkaline minerals is going to take place. Some of the byproducts are carbon dioxide, but they will come right out of the water.

Initially, the Ph will be very low, but within two or three days, that will rise back up. So, from 8.5 you may be able to take it down to 6.8 – 7.0 depending on how many caps you put in, and the baseline Ph balance of your water. This first mixture is a test to help you figure out what your unique ideal mixture will be. For example, if you put in two caps worth of acid and figure out that your Ph is 5.5, then the next time around you just add one. On the other hand, if you add two caps worth of acid and you’re still at 7.8 or 7.9, then you will want to add three caps full.

Once you figure it out, the aquifer is not going to change, so you will be able to repeat the process without this testing phase. You simply fill up your tank, put in the right amount of acid, and you’re done.


 Adding the Mixture to Your Tank


The easiest way to add the newly balance water to your tank will be to use the pump, and the custom PVC valve adaptor we mentioned earlier. Why do you need the adaptor? When you plug in the pump water is going to come rushing out immediately, but if you have the adaptor on the end of the hose you can have more control. Just make sure the valve is shut before you turn on the pump.

When you go to fill up your tank, all you need to do is hook the adaptor onto your tank, open the valve, and water will begin going in. Once you’re done and the tank is filled you can unplug the pump and shut it down. Unscrew the adaptor from one end of the hose, and then unscrew the hose from the pump and you’re all done. That’s how simple it is. We hope this helps you enjoy your hobby even more and makes it easier for those of you who can’t have Discus or Altums because of your high Ph levels.


 Important Advice


Don’t skip any of these steps! If you try to put the muriatic acid straight into your tank without letting it sit and react away from the fish, it’ll wipe everything out. It’s a cloud of death for the fish so make sure the reaction takes place away from the fish. Please keep this in mind.

Remember that muriatic acid is a very strong chemical, so be aware of this when deciding where you are going to make the mixture. If you drop any on an interior floor like carpet, hardwood, etc. it may ruin the floor. Also, if you get any on your hands or exposed skin, you’re not going to burn instantaneously like in the movies, but it will sting a little. Just stay calm and wash the area with water and soap.


 Thank You for Reading!


As always, we hope that this article will help make your tropical fish hobby easier and more enjoyable! Be safe when working with these chemicals but remember to have fun with it as well. This is Gabe Posada, and thank you for coming to Jack Wattley Discus. You can find out more about us on Facebook, Instagram and YouTube. Make sure to check in regularly on our website at Wattleydiscus.com where we are always adding more fish, gear and helpful content!

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Wattley Discus Admin


  1. David Lanteigne

    Doesn’t muriatic acid raise the TDS of your water to levels that wouldn’t be conducive to breeding discus?

      • Jim W

        What PH are you recommending to target? 6 – 6.5 ?


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