Skip to Content

Can Too Much Water Conditioner Kill Fish? It Can Bind Oxygen!

Can Too Much Water Conditioner Kill Fish? It Can Bind Oxygen!

Sometimes, the things we do with the best intentions backfire in the most unexpected ways. Actually, I am reminiscing about when I dumped a whole bottle of water conditioner into my tank with my fish present! 

Thank heavens my fish survived without any complications – but can too much water conditioner kill fish? Or is it, a matter of fact, harmless?

Keep reading to find the answers! 

Can Too Much Water Conditioner Kill Fish? 

Yes, too much water conditioner can kill a fish. But you’d really have to dump an entire bottle of conditioner into the tank like I did or even more. Even then, most fish wouldn’t bat an eyelid (like they have any!). So in most cases, using water conditioner in slightly larger doses than recommended is harmless, but I’d still not recommend doing so. That’s because it will bind to the oxygen present in the tank and suffocate your fish. 

Now, young and healthy fish can most probably fight through it. But if you have old fish with compromised immunity, they might get victimized. Therefore, we cannot completely rule out death by suffocation due to overdosing water with a conditioner. 

Even the Seachem Prime conditioner label instructs that using 5 times more than the recommended standard dose is acceptable to detoxify nitrite in emergencies. So, I guess there is some room for error after all. Don’t worry! 

Still not convinced? Here’s what one author on a fish forum has to say: 

“I have a 75-gallon tank. And instead of adding 5ml per 10 gallons, I added 20 ml! But my angelfish were good, and so were my gouramis and cichlids.”

So, you see, adding too much water conditioner isn’t downright harmful. But you still should strictly adhere to the guidelines written on the labels to be on the safe side. 

Now that we have tackled the main query let’s look at some other bits and pieces of information on water conditioners that you should know! I’m not assuming you don’t know them yet, but there is nothing wrong with a bit of revision, right?

3 Types Of Water Conditioners 

At the time of writing this article, there are basically 4 different types of water conditioners that are commonly used in the fishkeeping hobby. They are: 

  • Dechlorinator 
  • Chloramine neutralizer 
  • Complete conditioner 
  • Reverse osmosis water conditioner 


As the moniker gives away, the dechlorinator helps to instantly get rid of chlorine. However, they’re not adept at removing heavy metals and ammonia. 

And since these don’t tackle ammonia, they’ve pretty steeply gone down in the popularity charts. 

Also, note that if your tap water contains chloramine, using a dechlorinator can lead to quite a dramatic ammonia spike! 

Although not used widely these days, CrystalClear Vanish is the most popular dechlorinator brand in the hobby! 

Chloramine Neutralizer 

A chloramine neutralizer is a lot more versatile than a dechlorinator. It can instantly remove chlorine, break down chloramine, and neutralize the ammonia.

It makes the water less toxic in the following ways:

  • Binds the ammonia molecule, making it harmless for the fish 
  • Converts ammonia into ammonium that’s also not dangerous for the fish

Fritzpro is my go-to chloramine neutralizer that eliminates chlorine, chloramine, and ammonia in a jiffy without any hassle! 

Complete Conditioner 

When hobbyists mention conditioners, this is what they’re talking about 9 out of 10 times – and for good reasons! 

Complete conditioners are as versatile as they come. Here’s a shortlist of what they can do:

  • Neutralizes ammonia 
  • Gets rid of chlorine 
  • Eliminates copper 
  • Detoxifies heavy metals 
  • Protects fish’s slime coat 
  • Buffers pH

This list isn’t even conclusive. Complete conditioners can do a lot more, depending on the brand. 

Our personal favorite at Urban Fishkeeping is the Seachem Prime. I don’t even have to tell you why I recommend this – you already know! 

Reverse Osmosis Water Conditioner

Well, as a matter of fact, this isn’t actually a conditioner – it is a re-mineralizer. But manufacturers and hobbyists alike refer to it as a water conditioner. Therefore, I have decided to include it. 

Reverse osmosis removes chloramine, chlorine, and all other nasty stuff found in tap water. Thus, you don’t have to use any other water conditioner with RO water. 

But here’s the other side of the coin – it also removes the good stuff like magnesium, calcium, and potassium crucial for a healthy tank ecosystem. 

So, An RO water conditioner can help replenish these missing minerals. 

Recommended Readings!

Black Mold In Fish Tank | Effective 4-Step Treatment

How To Save A Dying Cichlid? 4-Step Guide

What Does Blue Light In Fish Tank Do? What About Red And Green?

How Often Should You Use A Water Conditioner In A Fish Tank?

You better stock up on water conditioners! You have to use them every time you perform a water change or top off your freshwater tank. So, if you change the water weekly, you should use it weekly. If you change water biweekly, you should use it biweekly and so on! 

If you skip using a water conditioner, it’s equivalent to dumping toxic chemicals into the fish tank. 

And by the way, if you’re in the process of cycling a new tank, you will have to add water conditioner pretty much every day until the tank has finished cycling. 

Can You Use A Water Conditioner In A Saltwater Tank?

No! You shouldn’t use a water conditioner for a saltwater tank. Leave them for freshwater tanks only. That’s because water conditioners don’t remove chloramine and heavy metals per se. Instead, what they do is neutralize and render the compounds, so they’re harmless to your fish. 

So, this process creates a favorable environment for algae and cyanobacteria to proliferate by providing them a food source. 

Therefore, wherever possible, we recommend using the reverse osmosis/deionization (RO/DI) process for saltwater aquariums. 

However, sorry to contradict, but it’d be wise to keep a water conditioner handy for emergencies where you need to treat tap water immediately and don’t have any alternatives. 

Can You Use A Water Conditioner With Protein Skimmer?

And for those of you with protein skimmers, don’t use a water conditioner until it states explicitly that it won’t cause the skimmer to foam. 

When in doubt, simply assume that your water conditioner is not safe for protein skimmers. 

Can You Use A Water Conditioner With Fish In The Tank?

So many fish
Credits: Toshiyuki AIMI (Creative Commons license)

Yes, you can safely use a water conditioner with a fish present in the tank. This is because they’re specifically formulated to be used in the presence of fish. However, if you have a small tank, consider removing the fish first. This will ensure the conditioner diffuses equally across the entire tank. 

From what I found on the forums, two reservations that people had in regards to using water conditioner in fish’s presence are:

  • The conditioners are chemical at the end of the day. It could be harmful if the fish ingest them. 
  • Since water conditioners remove toxins from the water, they can find a new home in the fish’s bodies. 

While these are two perfectly reasonable concerns, allow me to quickly debunk them for your peace of mind. 

These concerns are unfounded for the two following reasons respectively:

  • Water conditioners are scientifically formulated to be safe for fish even when overexposed to these chemicals. 
  • Water conditioners work quickly. They are capable of neutralizing the toxins before they pose any harm to your fish. 

However, if you still aren’t assured, you can always remove the fish first. There’s no harm in that. And that takes us to our next question! 

How Long Should You Add Before Adding Fish After Conditioning The Water?

If you have an established tank, wait 10-15 minutes before adding fish into the tank after treating it with a conditioner. However, since most conditioners are designed to be used in the presence of fish, you can add the fish right away if you can’t bide time. 

While it’s unnecessary to remove the fish in the first place, some people prefer doing so, and it’s perfectly fine. However, the waiting period to add fish boils down to the tank’s size and maturity. 

Old Tanks 

You don’t have to wait any more than 10-15 minutes to add the fish back for old tanks. By this time, the conditioner will have fully neutralized the harmful compounds and make the environment safe for your fish. 

New Tanks 

I know it’s a lot of time, but tanks take around 6 to 8 weeks to fully cycle. And you have to add conditioner every day or every other day while the tank is being cycled. Water conditioners will not speed up the process. So naturally, you’ll have to wait 6-8 weeks to add fish.

Why Is Water Conditioner Important For Fish?

Let me tell you a few facts. According to the FAQs published by Duke University, exposure to a higher concentration of chlorine can instantly kill a fish. And according to WHO, drinking water available to most of us contains at least 0.2-1 mg chlorine per liter. So I guess it’s self-explanatory now! 

Even at the lower range, that much amount of chlorine can be straight-up fatal for your fish. 

And while chlorine can evaporate to an extent naturally, chloramine, another compound used increasingly to treat tap water, is actually a combination of chlorine and ammonia. And unfortunately, chloramine doesn’t just evaporate. 

And lastly, I’m sure you’re well-versed in how harmful ammonia is for fish. 

So, yes, this is why a water conditioner is essential for fish! 

How To Add A Water Conditioner To An Aquarium?

The two most commonly used methods to condition aquarium water are:

  • Using a container 
  • Using a hose 

Using A Container 

In a container that houses the water going inside the tank, add the conditioner as instructed. Then, swirl the water with a clean stick or spoon before pouring it into the tank. 

Using A Hose 

If you use a hose to do water changes, you can add conditioner to the tank even as the new water enters the tank. Then, once you measure the amount, slowly drip it into the water as it streams into the tank. 

Final Words: Can Too Much Water Conditioner Kill Fish?


Yes, too much water conditioner can kill fish. But only if you really went overboard and dumped entire bottles of the conditioners. Even then, there’s a good chance that your fish will survive. 

Luckily, with water conditioners, there’s plenty of room for mistakes. They’re designed to be non-toxic for fish, even when used in large quantities. 

However, the water conditioner will bind with oxygen and potentially suffocate your fish. We can’t rule out that. 

Recommended Readings!

Meet The Most Expensive Freshwater Fish That Costs $400,000

5 Best Nano Skimmers in 2022 | Honest Reviews

5 Best 5-Gallon Fish Tank Filters In 2022 | Honest Reviews

What To Do When Your Fish Is Dying? Try These 5 Things!

How To Save Dying Fish After Water Change? Do These 6 Things!