Bacteria in a Bottle

When To Add Bacteria To Aquarium – (Top 4 Times)

When to add bacteria to aquarium, there’s really only 4 distinct situations when you should add bacteria directly into your system. There’s also a very specific scenario when you shouldn’t be wasting your money. In this article we’ll cover them all.

When To Add Bacteria To Aquarium

  1. During a brand new tank cycle
  2. When adding new fish
  3. During an ammonia spike (Together with Seachem Prime or any other ammonia detoxifier)
  4. During a filter cleaning or filter replacement


Why Add Bacteria To Aquarium

The beneficial bacteria in your tank is what’s keeping your tank functional and habitable for your fish. Without them our fish would die from ammonia and nitrite poisoning. Every tank must have beneficial bacteria in it. How it naturally gets into your tank, I have a great video on the subject, watch here.

Depending on what level of aquarists you are you either understand this fully or you have no idea what I’m talking about. It’s ok, we were all beginners at some point! So If you’re in the ladder then I highly suggest you check out my Beginners Playlist on YouTube full of videos to get you up to speed on the hobby.


Add Bacteria During A Tank Cycle

For the purposes of instruction I’m going to be referring to Seachem Stability as my go to source of bacteria in a bottle.

But there are plenty of similar products that will accomplish the same if you cant get a hold of Stability. Like Api Stress Zyme, or Fritz Turbo Start, just to name a few.

Adding Stability to a brand new tank setup is going to help in cycling your tank. This bacteria in a bottle bypasses the time it takes for bacteria to grow naturally in your tank. But with that being said let me make something perfectly clear.

You don’t NEED to add bacteria from a bottle during a tank cycle.

It’s just a widely used method of speeding up the amount of time it takes for your tank to cycle. Some aquarists prefer not to use any chemicals in their tanks and cycle the traditional natural way. That’s completely fine, to each is own.

If you’re a little impatient like me, its totally safe to boost your cycling time by adding stability. Its so safe that you can even add fish immediately to a new uncycled tank by using Seachem Stability in combination with Seachem Prime.

Yea that’s right, I said that – This tank is living proof

Now this leads me into when Not to use stability so you can stop wasting your money.


When NOT To Add Bacteria To Aquarium

When your tank has fully completed the nitrogen cycle, meaning you no longer have ammonia or nitrite in your tank, you do not have to continue dosing with stability, or any other bacteria in a bottle. Its unnecessary at this point because your tank has already grown enough beneficial bacteria to sustain your tanks current bio-load.

So save your money until you’re in situation number 2 – Adding new fish


Add Bacteria When Adding New Fish

Adding new fish will increase the bio-load in your tank. More fish , more poop, more ammonia. The current levels of beneficial bacteria in your tank can only consume the current levels of ammonia. When you add more fish, adding more ammonia, you need more bacteria.

Now this additional bacteria you need will grow on its own with time, actually pretty quickly. But during this time your fish will be exposed to this additional ammonia your current bacteria can’t handle. And the more fish you added, the more new ammonia there is.

Just like when cycling a tank Adding Stability when adding new fish will give your current levels of bacteria a boost helping to handle that increase in ammonia.

Similar to the reasoning of adding bacteria when you add new fish is going to be reason number 3, during an ammonia spike.


Add Bacteria During An Ammonia Spike

Yes an ammonia spike can occur when adding new fish but it can also occur for many other reasons. Like continuously over feeding, finding a dead fish or decaying plants in your tank, or possibly over cleaning your tank and killing off some of your beneficial bacteria.

There’s no way to tell when you’ve got an ammonia spike. Unfortunately the first sign or symptom is usually death. If you’re lucky enough to have tested your water and noticed the ammonia spike before any fish death, then…yea, you’re lucky.

In this scenario I recommend the following in this order.

  1. Add Prime
  2. Water Change
  3. Add Prime Again
  4. Add Stability


Add Prime immediately to detoxify that ammonia spike while you prepare for the next step which is a water change. A big water change, about 50% is best to ensure we dilute as much ammonia as possible.

When adding in new water add Prime once again and also add Stability.

This is a great time to ensure there is enough beneficial bacteria in your tank to handle whatever has caused the ammonia spike. Some may see this as unnecessary at this point, since you removed a lot of the ammonia during the water change, but I’d rather stay on the side of being safe rather than saving a few sheckles and not dosing with Stability. It’s definitely not going to hurt anything at this point…so why not?


Add Bacteria During A Filter Cleaning Or Replacement

Like referenced before over cleaning can kill off beneficial bacteria. Your filters are going to house the most bacteria than any other place in your entire tank. So being diligent in keeping them alive in here is important.

If most of you are like me I try to clean my filters in the most efficient way without killing off any bacteria both by using tank water to clean my sponges and also hardly ever touching the bio-media itself. Maybe just a couple of dunks in tank water and that’s it. Here’s a great article on cleaning the Fluval FX6 and cleaning the Fluval 07 Series.

But there is still a very high chance that SOME of your beneficial bacteria will die off. Not all, but some.

Like wise when you replace a filter you should be transferring all of the bio-media from the old filter into the new one in order to preserve as much of the beneficial bacteria you already have…but some may die on you.

Which is why this is the perfect time to add bacteria just in case there was a reduction in your bacteria levels, the Stability or Stress Zyme or Turbo Start will help to replenish whatever was lost. Again, safety over savings.


Many are under the impression that Bacteria is something that needs to be added often, like weekly, or during every water change. That is simply not the case. Save your money by only dosing bacteria during these 4 scenarios and your tank will remain clean and healthy while you keep some extra sheckles for everything else your fish need! 😁

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