Can I mix this with API Quick Start and API Stress Coat+ in a gallon every time I do water changes weekly? Or just pour it directly in my 5.5 tank?

In short, you don't need the Stress Zyme if you already are using the Quick Start. Here's a longer answer:The API Stress Coat is primarily a de-chlorinator and has aloe added to help maintain a healthy slime coat on the fish so this should always be added to the water and mixed before adding to the tank. The API Quick Start is meant to jump start the biological cycling of a tank and is only needed for new tanks or potentially semi established tanks that have a spike in ammonia and nitrite levels which could be caused by adding more fish. You can stop using this once your water chemistry has stabilized. API Stress Zyme is very similar in function to the Quick Start and is generally chosen to improve water clarity or stabilize chemistry in more established tanks. You don't need to use both simultaneously and would probably never see the difference compared to using just one. On another note, I always add my bacteria after there is no chance there is any chlorine so they have a better chance of proliferating. I would add either the Quick Start or the Stress Zyme the day after a water change, directly into the tank.

can i mix stress coat, stress zyme and tap water conditioner? if so what amount of each should i mix? doing this harm my fishes?

Stress Coat and water conditioner is the same. ( stress Coat is water conditioner ). if you use both at the same time that you double it up. Maybe it is nothing will happening . But, it is not necessary to do that.

How long this product can be stored before it expires? Also, would its effectiveness reduce during long time storage?

As for length of time you can store, I use it weekly and it lasts for about four months or so. Does not seem to lose effectiveness in that time.

What is the expiration date on this Stress Zyme? It seems very inexpensive.

There is an expiration date on the bottle, however, these are live bacteria and once the bottle is open the shelf life is cut in half. Same as Seachems Pristine. Buy the size bottle for your tank. There is 250ml and 500 or 750ml, depending on the brand. My personal and professional advice is buy the smaller one 1st and see how much you go through, follow the instructions completely. They work well, keeps the glass cleaner longer. Also very important, make sure the aeriation is adequate and they say to change the filters 1st. If you have the $$ go for it. Best and least expensive and just as sufficient, is to change them half way before you normally change out your filters. API Stress zyme seems to keep its life span quite a while after opening. But trust me, you'll use it up way before it expires. Compared to the other similar products, this one seems to leave more of a brownish pile on the corners or underneath Ornaments, whis in turn will have to be vacuumed, netted or a baster for cooking depending on the size of your tank. 👍

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Reviews

S**R

10/10

Works really well with my tank keeping the water clear and helping reduce sludge on the filters which helps maintenance and keeping it running longer

5.02.2026

A**6

Amazing product. Really works.

I use this weekly, RELIGIOUSLY. I do not miss a dose. This is my tank today, having not touched the filter in 18 months. (Fluval FX6 filled with only biohome filter media and polishing sponges.) I’ve only changed out the live plants when needed (pothos houseplant clippings) and used the magnetic algae glass scraper when needed. It’s a 75 gallon tank. I8 MONTHS!!! I highly recommend this product. Zero odor, zero nastiness.

13.07.2025

J**N

Great for my aquatic frogs

I use this religiously with my African dwarf frogs! They are still kicking strong after 3 years so it must be working!

8.12.2025

G**O

Clear water

It works great. Keep my water crystal clear.

4.02.2026

C**G

... used Stress Zyme for quite awhile and had relatively good experiences with it

I've used Stress Zyme for quite awhile and had relatively good experiences with it. More recently though I've moved to Seachem Stability and found that I prefer it. The Seachem product is more expensive but I've had great success with their line of products and find that Stability works great. Having said that I don't' want to give a negative impression of API's Stress Zyme. It does a good job of establishing and maintaining your biological filtration which is solely responsible for keeping your tanks nitrogen cycle in check. The Stress Zyme, like other "bottled bacteria", is a blend of anaerobic and aerobic bacteria and a "slime coating" agent that helps keep fish happy and healthy. The bacterial agents don't seem to be as "potent" as some others I've used like I mentioned earlier. But, the slime coat portion is more noticeable. When Stress Zyme goes into the water you can see that it has an almost oily consistency that rapidly dissipates into the water column and I'm sure does a good job of keeping your fish... hmm... lubricated (for lack of a better word). Water parameter tests have come up good with API Stress Zyme and there seems to be no negative effects on any of my fish or plants from using or even overdosing it. It's relatively inexpensive and does a good job. If you can't afford Seachem Stability (which I think is a better product) I wouldn't hesitate to recommend Stress Zyme.

29.03.2015

A**S

Good 👍

Cleans good fish tank.

8.11.2025

D**E

Good value.

It works.

3.01.2026

M**I

Awesome

It makes fish feels better and more active more comfortable, it makes the water clear and nicer looking. Stop bad smell. Makes the top water safe. It Lower the PH lever.

21.09.2025

S**N

Have used this product religiously on my water changes and don't ever see that changing

16.08.2025

S**M

Producto muy recomendable!el agua no se enturbia para nada,hay que tener un buen filtro,el mio no funciona bien y el agua no esta sucia pero huele mal por el filtrado,el producto es buenisimo.

21.04.2020

S**A

I love the brand

2.08.2023

D**S

I was having some issues controlling nitrites. Used it, two days later, down to zero and stable. I don't see any issues with my Ph, fish, snail, shrimp and plants. I'll keep dosing the water as instructed.

27.02.2024

S**E

My regular go to solution after water change.. this has helped my ponds as well as big tanks for maintaining good bacterial colonies in sump and canister filters

22.08.2025

ASIN	B0002AQLJW
ASIN	B0002AQLJW
Best Sellers Rank	#3,895 in Pet Supplies ( See Top 100 in Pet Supplies ) #21 in Aquarium Water Treatments
Brand Name	API
Color	Blues & Purples
Country of Origin	United States
Customer Reviews	4.8 4.8 out of 5 stars (12,041)
Date First Available	June 20, 2004
Date First Available	June 20, 2004
Department	Unisex-Adult
Department	Unisex-Adult
Directions	Use weekly for a healthy, clean aquarium and to maintain a strong biological filter. Shake well. Using dosing cap on bottle, add 5 ml per 10 gallons (38 L) of water. For new aquariums and to help boost the biological filter, double the dose at start-up and use for 2 additional weeks.
Is Discontinued By Manufacturer	Yes
Item Dimensions LxWxH	10 x 10 x 10 inches
Item Package Dimensions L x W x H	5.87 x 3.82 x 1.38 inches
Item Weight	136.08 Grams
Item model number	56C
Item model number	56C
Manufacturer	Mars Fishcare
Manufacturer	Mars Fishcare
Manufacturer recommended age	1 month and up
Material	Plastic
Model Name	STRESS ZYME, 4 OZ
Number of Items	1
Product Dimensions	10 x 10 x 10 inches; 4.8 ounces
Size	4 oz
Style	Freshwater
Target Audience Keyword	fish

API STRESS ZYME Bacterial cleaner, Freshwater and Saltwater Aquarium Water Cleaning Solution, 4 oz

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