How much water should I change in my fish tank?

How much water do I change is a question I see a lot in forums and on Facebook. In this video I explain in simple terms how much water to change, the Nitrogen cycle and how to test aquarium water.

Things I talked about in the Video:
Tetra 6 in 1 Test Strips

Tetra Ammonia Test Strips

API Master Kit

Check out my website to order fish:

If you have any questions or would like to buy any fish, please email me at

By MFR Apparel here:


**Products I use or have used in the Fish Room**
API Freshwater Master Test Kit

Tetra 6 in 1 Test Strips (I use these)

Tetra Ammonia Test Strips ( I use these)

Seachem Prime

Seachem Safe

Python Water Change System

Bacto Surge Sponge Filter

Cheap China Sponge

Lee’s Specimen Container

Prazi Pro

API General Cure

Ich X

Blue Airline Tubing

Rocker Chicks by Audionautix is licensed under a Creative
Commons Attribution license (

23 thoughts on “How much water should I change in my fish tank?

  1. anthony stevens

    Mine leaves the tap at 40ppm nitrates! I actually change as little as possible because of this and use heavily planted tanks. Salvinia is awesome at stripping nitrates out. The API test strips are RUBBISH. Tetrafin is brilliant. NT labs is a better liquid test kit. Way easier to read.

  2. mranexmrsmopslilgirl

    Loved the video as always, I have done a lot of watching YouTube fish FAM and have also read a bunch then taken all advice an found what works for me …
    I change 50% of my water maybe a lil more every week it may be a day or so over but who's counting and I look at my fish if they r not as active as the day before then I may change their water a few days early .. This works for me ..
    I have a 4ft long x 15 inches wide x 18inches tall with goldfish, white clouds plus a hodgepodge of various small tetras. I feed once a day if I'm home I split that 1 big feed into 2, I have algae growing on the back and sides an the bare bottom, bunches of algae covered fake plants 3 big sponge filters plus 2 small ones and an never clog air stone all run on 2 air pumps my fish are happy so I am happy …. So I say again this all works for ME …

  3. Anthony Ragan

    Good video. It's always handy to review the basics. I do 20% weekly, sometimes twice weekly. Problem I ran into early on was changing so much water that I was starving the plants of nitrates. I like to keep them between 20-40 ppm.

  4. EJ Fishes 76

    I only test when/ if I have an issue. I have a routine down for the water changes, my heavily stocked 75g gets 50% weekly for example as this has worked best for me. However one of my 10g that has my blue/ green Moscow guppies and is heavily planted is once every 2 weeks at 25%.

  5. Damian Bloodstone

    Great vid on the topic. When I had my 10 gal tank, I changed two gallons on Wed. and five on Fri. After it became mature (over two years old), I cut down to the Wed change due to the plenum and the power filter I ran together in my planted tank. Sadly, a hurricane power outage of a week killed it and most of my fish except my betta.

  6. Catfish Cave

    I have a hermetically sealed tank that I haven't changed any water inside it in 42 years. My ghost cats, ghost knife and ghost fish are all fine… they look just as ghostly as ever…
    Seriously though, it is often said not to change more than 50% because a newb (hey, relax people, we were all there once) may not understand what is going on in the tank and may change over 50% when it is NOT ADVISABLE to do so. For example, you haven't changed water in 5 months and your ph and KH have dropped dramatically and when you change too much water the pH and KH instantly rise dramatically, potentially causing pH shock, and ammonia problems, as free ammonia is more prevalent at higher pH levels.
    As for me… I really have been in the hobby 42 years… and I read a lot… I mean a whole lot! I try and understand the chemistry of water and the nitrogen cycle. And I always do 90-99% water changes. (sometime I overfill the tanks – oops – sorry honey, it won't happen again. Hahahahahaha!) So like Michael said, please do your homework on your own tank. Once you know how fast it builds up nitrates, you'll know how often and how much to change it.
    This message was NOT paid for by a slow roasted brisket from Michael's Fish Room.

  7. Barbara Jackson

    Very good explanation. I try and change 50% weekly and twice a week on the heavily stocked Guppy tanks. Has worked for me so far. I do test the guppies pretty much weekly because of the changing population. On my community and species only tanks I test way less often as they’re more stable tanks. I try to keep them all around 40 nitrates because they all have a lot of plants.

  8. bald and dangerous

    thanks for the info michael,really helpful, i bought the tetra test strips as well ,did you check out the website i mentioned ? anyway thanks and all the best…………….dougie from the uk

  9. George Dekker

    My fish have never been happier… since I stopped changing water. What I do is top up. And most importantly, dose heavy with fertiliser that does specifically not include nitrate.
    about 4 months since the last water change.

  10. Lumpydog

    Another great video. I agree with your "When to do water changes" answer. I do weekly water changes because it's my routine. I change 20 – 40% at a time depending on stocking levels of each tank. I know with my schedule that if I miss a week my Nitrate levels will still be in an OK range. My Nitrate levels typically fluctuate between 10 – 40 ppm in my planted tanks between water changes. Anything below 10ppm and my plants don't do well. Thanks for putting out the videos. Keep them coming. Cheers. p,s. Is your basement testing lab ISO 17025 certified (LOL).

  11. Bob Caylor

    This wreaks of the Illuminati. LOL

    Seriously, I use test strips regularly now, after seeing Cory debunk the API and Tetra Strip myth. They read the same. I have used API to verify a reading on occasion. I change the amount of water based on the readings. I keep some tanks at different levels, such as my heavily planted 40 breeder's Nitrates between 10-20. It's free fert. Very good topic and explained so us other dummies can comprehend.

  12. Mr Possy

    I need a camera too, which one are you planning of getting , what would you recommend to start off with im not to familiar with cameras. Thanks for another great video.

  13. Aquarium Adventures

    Not to be picky – but there is a bacteria that gets rid of Nitrate. It's just not very easy to cultivate in an aquarium – but it's the reason products like Biohome and the like exist.

  14. Chris Bright

    Second video I've watched. Great stuff and subscribed. Only thing you didn't mention is plants eating nitrates. Those Facebook groups can be a slippery slope when you comment on posts. Every expert in tge world may flood in and insist that you are wrong without any substance to support their argument. It can get crazy.


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