Do (and How) They Work – API Quick Start VS Tetra SafeStart?

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There’s an ongoing debate among fishkeepers about whether Tetra’s SafeStart and API’s Quick Start even work.

IF they do, which one is more efficient?

What is the difference between Tetra SafeStart and Tetra SafeStart Plus anyway?

Starting a new tank can be stressful for both you and your new fish buddies.

The logic behind these products is solid, but that’s in theory.

Is there a safe dose or an overdose?

Should you do a fishless cycle?

What’s the reality? The good news is I have tested them both…twice.

I’d be more than happy to show you my results and point you in the right direction.

Shall we?

Which one to choose if any – API Quick Start versus Tetra SafeStart?

Both products claim to have live nitrifying bacteria that will speed up or reinforce your nitrogen cycle.

They contain two sets of bacteria stains – one that turns the ammonia into nitrites and one that turns said nitrites into harmless nitrates.

Here’s the truth about the Tetra SafeStart vs API Quick Start comparison:

Both Tetra Safe Start and API Quick Start will work, given that they are applied in a correct manner. The cycling of a new tank will speed up significantly but it won’t happen overnight.

You can realistically expect a fully cycled tank at the end of the second week (10 to 14 days) after application. Dosage plays a major role in success.

However, following the instructions on the back is not something that will help, as they are pretty vague.

It is rather inconvenient that the instructions on both are not helpful.

After experimenting hard I’ve managed to highlight what strengthens your chance for success, eventually finding a process that, in my opinion, is foolproof.

I ran two tests on both before actually using them in a real fish tank project.

The only disappointing part is that they will not cycle your fish tank the same day.

Also by “add fish instantly” they don’t mean all of your fish.

How to use them and make them work?

After running a couple of tests I am confident to share my success formula with you.

Going through hundreds of forum threads and speaking with fishkeepers I know, I did find confirmations of my findings.

This means that my logic was correct.

Firstly you’d need to get the right bottle of bacteria.

Safe Start and Quick Start both contain live bacteria.

Both brands are claiming no refrigeration is needed.

The perfect temperature for the bacteria’s shelf and in-water life would be between 40°F and 80°F (5°C to 25°C).

Going beneath or above that range may spoil it, by killing the microorganisms and rendering the product useless.

Trusting your local fish store is okay, but I do prefer getting mine over or Amazon (link to them, that will open in a new tab). For the record, Chewy is an online store that specializes in pet supplies, so they really know how to ship the bottled bacteria properly and in the right conditions.

Anyway, if you do insist on getting from your local market make sure that they were safely stored and aim to get the most recently shipped ones (with the farthest expiration date).

Some instructions before you start are:

  • Get a bottle that has been manufactured as recently as possible – The newer the bottle, the better. Also, get at least two bottles, I will explain why later.
  • Choose a bottle meant for a larger aquarium than yours – For me, it worked best when I used the 3.38 Oz bottle of Tetra SafeStart Plus for my 20 gallons, and also when I doubled the dose recommended for the API Quick Start.
  • Make sure the ammonia is not already deadly high – everything above 2.5 ppm of ammonia will be harmful to your fish AND the bacteria. Before you start with the nitrogen cycle you need the ammonia lowered as much as possible.

With that out of the way, you can start cycling your aquarium.

Follow these exact steps to properly use Tetra SafeStart or API Quick Start:

  1. Dechlorinate your water no less than 24 hours before adding the bacteria.

    Use a dechlorinator.

    Leave the filters running during that time.

    Chlorine will kill the not well-established cycling bacteria.

  2. Shake the bottle of bacteria hard.

    This part is really important.

    Shake the bottle really well before adding the bacteria.

  3. Pour in double the recommended dosage.

    For Tetra users just add the WHOLE bottle of bacteria to your aquarium.

    Add it all.

    It’s beneficial bacteria. The more the better.

  4. Add 1 SMALL fish per 10 gallons of water.

    This should be done shortly after you’ve poured in the bacteria, within a maximum of 2 hours.

    The proportion is what worked best for me.

    By definition, this is where most people make a mistake.

    Adding a fish per 10 gallons of water is the safest way of controlling the ammonia levels.

    It’s true that you can stock the tank up, but you’d need very clean fish (ones that do not poop as much) and you’d have to feed them very carefully to either not overfeed (leaving extra ammonia work for your bacteria) or starve them (being too cautious not to overload your tank with ammonia).

  5. Feed your fish every other day.

    Test your water frequently, if you notice a spike in ammonia it’s okay to not feed your fish that day.

    Many fish can survive more than a week without food, so they will be fine.

  6. Don’t do water changes until the 14th day.

    If and only if the ammonia starts rising for no apparent reason you can do a water change to lower the levels down.

    Add another bottle of the product if that happens.

    This is why I told you to get a second bottle.

    However, there’s a solid reason behind this point.

    You’re probably using chlorinated tap water for your fish tank. In order to perform a water change you’d need to dechlorinate the water first, right?

    Water facilities in the more developed cities use Chloramine instead of Chlorine for disinfection.

    Chloramine represents the chemical bond of chlorine + ammonia.

    Seachem Prime (a commonly used dechlorinator), for example, breaks down chloramine to chlorine and ammonia, takes care of the chlorine, and detoxifies the released ammonia.

    Every product that claims to detoxify ammonia likely transforms it into ammoniUM.

    Ammonium is harmless to bacteria and fish alike, but the detoxifying effect only lasts for 24 to 48 hours.

    After that, the ammonium turns back into ammonium, which means you now have more of the latter in the cycling aquarium.

    The more Chloramine your water facility uses, the more the released ammonia after dechlorination, which could consequently harm your bacterial biofilter if the contents turn out to be too high.

    It’s important to note that this only affects new aquariums that do not have an established colony of nitrifying bacteria.

    Anyway, another argument for not changing the water in the first 14 days of cycling (unless there’s a dangerous ammonia spike out of nowhere) is that studies suggest that nitrifying bacteria use ammonia instead of ammonium for their source of energy.

    Continuously using a dechlorinator that turns ammonia into ammonium could actually slow down the nitrogen cycle in your aquarium even further. The nitrifying bacteria would not be interested in the latter and will not be stimulated to multiply further.

    This can easily turn into a vicious circle and a never-ending supply of Prime for a new, non-cycled fish tank…

    If you’re using bottled bacteria you’d want your fish tank to cycle as soon as possible, right?

    Tip: The best way to avoid all of this is by having a separate batch of dechlorinated water to use for water changes during aquarium cycling. The “emergency batch” should be dechlorinated at least 24 hours before use. Add a little bit of bottled bacteria to it to make up for the residual ammonia and it’s good to go.

    Suggested Read: How Aquarium Fish could Die After a Large Water Change

    Despite the described scenario Seachem’s Prime still remains a fantastic option for water dechlorination in a fully cycled aquarium. I’d recommend it to anyone who is using tap water for water changes. The residual ammonia from breaking down the Chloramine would be negligible to the already-established bacterial colony in a mature tank.

    Anyway, after 14 days of cycling, you can perform a water change the regular way.

  7. Don’t test the water for the first 2 days.

    It’s okay to test it whenever you want but that is something that I stuck to throughout my tests.

  8. Turn the UV lights off for the first day or two.

    Ultraviolet light does affect the bacteria in a negative way.

    For it to successfully establish I’d strongly recommend not turning those lights on the first day after the application.

Keeping the fish tank cycled

After the second week you can gradually add fish, but of course, don’t add 10 at a time.

When doing the first water change the ammonia will go up, as there is ammonia in tap water, but I wouldn’t worry about it that much.

The levels should be quickly back to normal within the next 12 hours or so.

Don’t freak out if you don’t see your nitrites spike when water testing.

If you’re using Tetra’s SafeStart the process will skip the nitrites building up and will directly build into nitrates.

Don’t worry if your aquarium becomes cloudy at first.

The water will get clear within two to three days or a week at most.

Seeing cloudy water in a new aquarium at the beginning of its Nitrogen cycling is completely normal and it means that different bacteria are establishing their hierarchy.

Visit the link if you’d like to understand the process in depth. Understanding aquarium microfauna is, in my opinion, a core component of long-term success in fish keeping.

And that’s not an overstatement.

Which one should you choose? What’s the difference?

This is not one of those posts where I discuss the pros and cons of both products and leave the choice to you.

I have a statement:

Both can be (successfully) used for a start but If you’re starting a brand new empty tank and want to establish an ammonia safe environment I’d recommend using Tetra SafeStart.

If you’re starting a brand new planted tank, doing huge water changes, or adding a lot of fish at once to an already cycled planted tank I’d go for API Quick Start.

Tetra’s better at handling the nitrites (it virtually skips them) and API will normalize your ammonia levels quicker which, in an ongoing aquarium, is more important.

High ammonia levels may result in your fish staying at the bottom of the tank seemingly gasping in despair (click the link for an in-depth explanation of this behavior in Bettas).

The API Quick Start is more efficient when you have a planted tank as it does not handle the nitrite levels as well as Tetra’s SafeStart. Live aquatic plants prefer ammonia and nitrite over nitrate as their source of nitrogen so, by using API’s product you will both speed up the cycle and let your plants feed on the nitrite.

Note: Between Tetra SafeStart and Tetra SafeStart Plus the difference is only in the concentration of the bacteria. I’m really happy with Using the Plus version, so the instructions will remain the same.

The saltwater alternative is called Bio Spira.

API doesn’t have a saltwater version, you just double the dose.

What’s with the mixed opinions then?

Honestly, it’s probably a human error.

Seeing how (upon proper use) the products kept proving themselves to me and others I spoke to, I can only conclude that.

Then again, the negative reviews pushed me to test them myself, before anything.


Fishkeeping is a patient hobby.

Whether you choose to go natural or use bottled bacteria products for starting a new fish tank, you will have to wait it out a bit.

There is no shortcut for that, there are only shorter cuts…

Tell me how things unfolded for your new aquarium in the comments.

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Thank you so much for this article! I’ve read it probably twenty times in the last two months. I received a new (and extremely tiny) 1.6 gallon fish tank and a betta as a birthday present back in March. Not knowing anything, and given poor advice from the pet store, the poor little guy died in 8 days from new tank syndrome. I was determined then to do a fishless cycle, and tried from March to the end of May with absolutely no results. I decided to try again in June using a hardier fish (I got a Panda Molly)… Read more »

Meg Brennfleck

Thank you for testing these products! I got my first Betta (Buddy, and he’s the coolest, spunkiest little thing) almost a year ago. The poor guy has been through a lot, mostly because his mom travels and falls a little behind on water changes. He also went through a significant relocation that sent him into a bit of a depression which I believe led to some fin rot. He’s overcome that, and now I’m worried he has Popeye, or maybe it’s just a weird growth on his face (I have no idea who I can even consult for something like… Read more »

Gary Gibson

Thank you for this post! After reading this I decided I would use safestart to cycle my new 75 gallon aquarium. I followed the directions exactly and (against all advice) started off with 6 Neon Tetras. I tested at 3 days and 5 days just because…. 0,0,0. Been feeding lightly… kind of surprised at 0 readings but I guess if Nitrates slowly build towards the 14 day mark that be good(?) the tank is well filtered, non-planted, fish seem happy (I will update regarding the Neon Tetras as well). I will wait patiently… anything else I should watch for?


Hey there! I got sort of thrown into fishkeeping with a platy brought to a gift exchange (live animals make terrible gifts but try telling that to this guy…). I’ve had the platy in a 10 gallon planted tank for 2-2.5 weeks now. I’ve done a few water changes in that time (about 30%). I’ve been dosing with API QuickStart as the bottle recommends. Just now tested the water for the first time (I didn’t order a test kit until I learned I needed one a week ago—there’s definitely a learning curve in fishkeeping!) and pH is about 7.5, ammonia… Read more »


Thanks for the info. I recently got a 50 gallon aquarium after about 15 years of not having one.
I followed your instructions, used the tetra tap water dechlorinator and tetea plus. Gradually added some tetra and danio glofish. Did a25% water change 3 weeks later. 2 months later I have 6 of each and 2 catfish. They are schooling, happy, and healthy.


I am using API Quick Start. All has been well in the tank for almost a week. But the nitrates have spiked. Should I do a water change even though it hasn’t been 2 weeks? And if so, how much water should I replace?


Researching the do’s and don’ts of fishkeeping is like trying to figure out which weather man to believe. Very aggravating. :\ I started up my 46gal bow front 4 weeks ago, added fish a week later… four Rosboras (two are very young and small), a small DoJo Loach, and a Rainbow. I only learned of fishless cycling after purchasing my fish and wish I would have went that route as my Rainbow died from the ammonia not even a week after purchase. The ammonia level was at 0.50-1.0. I paniced, did about a 15-20% water change and added some chemical… Read more »


Also, as today is Thursday, Jan 31st, the water change I performed was on Friday Jan 18. Was debating on doing a water small change change tomorrow.


I have multiple tanks but my concern is with my small 5 gallon. I have it set up for dwarf seahorses. I waited 6 weeks for it to cycle before ordering my seahorses but after ordering, checked and realized the salinity was too low. I added salt water and was surprised that my tank went up to toxic levels, 0.5. I tried several things in a panic! (water changes ect.) and finally today, I emptied all water, cleaned the filter, and then added cycled water from my 55 gallon tank. Now it’s reading safe but I’m a bit paranoid. The… Read more »

Anna Klingensmith

Hi, I started a new tank 10 gallon. I started it about a week and a half ago. All the levels are great and I’m getting fish tomorrow. My question is Should I add the whole bottle of safestart plus or the recommended dosage for adding new fish. When I started the tank I put safestart in, but have since added conditioner. I wanted to add the safestart plus to prevent new tank syndrome and to filter the bacteria. I’m not sure if I should add all or not. Thank you! Anna