Why big water changes? - The Planted Tank Forum
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post #1 of 17 (permalink) Old 06-05-2015, 08:41 PM Thread Starter
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Why big water changes?

I've seen quite a few threads where people recommend doing 50% water changes at least once a week. Why should we do such big water changes?

I work at PetSmart and I've always been taught that you should never do more than a 25-30% water change because you start taking out a lot of your good bacterias that keeps your tank healthy and stable. Is it different for planted tanks?

Just curious because I'm due for a water change on my new 29 gallon tank, not sure how much I should take out...
-Sara
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post #2 of 17 (permalink) Old 06-05-2015, 09:04 PM
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Basically removing the nitrates and replenishing minerals and such via fresh water. If your nitrates read 30 ppm, a 50% wc will cut them in half while a 25% wc will still leave around 20 pmm of nitrates in the tank.. there are other factors though. Heavily stocked tanks will require a little more attention while lightly stocked tanks can go a little longer. Here's a list of my tanks and what I do to them as far as wcs, keep in mind the high techs have lots of ferts that need to be cleaned up.
30long high tech- weekly 50-60%
20 tall ht- weekly 50-60%
20long low tech apisto pair tank- 30-40% every 8-9 days
7.5 ht- 60% every 4 days (heavily stocked and gets messy fast)
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post #3 of 17 (permalink) Old 06-05-2015, 09:06 PM
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There are a couple of reasons for big (50% ) weekly water changes in planted thanks.

First, doing big water changes really won't remove your beneficial bacteria as most of them aren't free swimming in the water. They live on rocks, decorations, driftwood, the glass on your tank, plants if you have them and mostly in your filter media, as long as you dechlorinate the water going back into the tank, and make sure no soap or detergent residue is in any of the buckets you're using for your water change, your bacteria colony won't be greatly impacted and will keep on cycling ammonia and nitrite just fine.

Most planted tanks have relatively high lighting which promotes fast algae growth, changing a lot of water helps deter algae growth. And finally most planted tanks are being dosed with fertilizers and nutrients to encourage plant growth, these nutrients can over accumulate (again promoting algae) so big weekly water changes helps to prevent the build up of certain nutrients from getting too high.

In smaller tanks doing those big weekly water changes isn't a big deal and takes little time. As you get into larger tanks it gets to be a bit more work. I've got a 10 gallon planted tank in my office at work. I come in early on Friday and within 20 minutes I've done a 50% water change, cleaned everything up, wiped down my glass and have everything put up because it only takes about 3/4 of a bucket of water (with substrate and decorations there's a little less than 8 gallons in the tank). Nobody I work with is even aware that I do it each week.
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post #4 of 17 (permalink) Old 06-05-2015, 09:07 PM
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lol
Big chain LFS have no clue what they're talking about from what I have seen. Take advice you get there with a grain of salt...
Bacteria that break down ammonia are grown mostly in substrate and filter bio media. Big water changes are beneficial IMO for the following reasons:

-remove excess nitrates in mass
-remove dissolved solids (waste)
-doing smaller water changes takes about the same amount of time.


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post #5 of 17 (permalink) Old 06-05-2015, 09:08 PM
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The bacteria is on surfaces in the tank and not in the water. Don't have to worry about that.

MY TANK: Planted 10g; 2 x 10W CFL; Fluval U2 internal filter; MGOCPM/black sand cap

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post #6 of 17 (permalink) Old 06-05-2015, 09:14 PM
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The bacteria is not housed in the water column but rather grows on the various surfaces in the tank. The glass, the substrate, and most importantly on the biological media contained in your filter. This is why very porous things (like lava rock and branded bio media) work so well because they have a lot more surface area than meets the eye. The bacteria live in all those tiny little crevices as they need a surface to live on. The water itself really has no effect on the bacteria (unless you count chlorine or other additives that are in the water which can kill the bacteria).

So long as you have an established tank containing cycled filter media you can safely do a 100% water change and not harm that beneficial bacteria. Doesnt matter if its a freshwater tank, planted tank, bare bottom tank or a saltwater tank.

I have multiple tanks and do at least a 50% water change in most of them weekly. I have three tanks that house discus and those get anywhere from 30%-80% water changes every single day.

I'm not sure who from that store provided you with this false knowledge; but this is likely why these big box stores get such a bad reputation!

Rich's Fishes
Curator of an ever growing fishroom that currently houses 30 different tanks. Most full of at least water....some even have fish!
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post #7 of 17 (permalink) Old 06-05-2015, 09:19 PM
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I will say that water changes that large aren't always "Necessarily". If you have a light bio load and aren't dosing, you're ok as long as you're reading 0ppm Amonia and Nitrite and <20ppm Nitrate. Smaller and somewhat less frequent water changes are fine as long as your parameters look good.
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post #8 of 17 (permalink) Old 06-05-2015, 09:39 PM
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As you can see by the responses every tank is different and should be treated as such. Water changes are dependent on quite a few factors and understanding these factors are imperative to the success of each tank.

The general idea of large 50% water changes is to keep the water column rid of excess nutrients that feed algae, but this can be combated by a simple lighting adjustment... a split shift of on then off then on will help deter algae growth.

Of course it really depends on the tank and whether it is planted, low tech, hi tech, lighting output...etc.

It is my opinion that there is no one specific regimen that should be prescribed to every tank as a blanket statement, but I agree that the big box stores know less than they should considering they are profiting from their supposed expertise...or is it by design.

I learned the hard way that I am only a water keeper!
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post #9 of 17 (permalink) Old 06-05-2015, 09:54 PM
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Quote:
Originally Posted by anewbeus View Post
......

It is my opinion that there is no one specific regimen that should be prescribed to every tank as a blanket statement, but I agree that the big box stores know less than they should considering they are profiting from their supposed expertise...or is it by design.
I suspect the chain-LFS advice is to benefit themselves.... I watched a guy have his water tested last weekend, from metres away I could see the colour of his ammonia tube, dark green. What did they do? (I eavesdropped)

Sell him a bigger filter. And suggest a 10% water change. I bet he's back buying more fish this weekend..... maybe a method to their 'madness'....
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post #10 of 17 (permalink) Old 06-05-2015, 10:26 PM
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Quote:
Originally Posted by Sarraa View Post
I've seen quite a few threads where people recommend doing 50% water changes at least once a week. Why should we do such big water changes?

I work at PetSmart and I've always been taught that you should never do more than a 25-30% water change because you start taking out a lot of your good bacterias that keeps your tank healthy and stable. Is it different for planted tanks?

Just curious because I'm due for a water change on my new 29 gallon tank, not sure how much I should take out...
-Sara
The 50% water changes is usually for people who dose fertilizer. Every week you'll do a 50% water change to reset the nutrient levels. For someone who has a fish only tank doing bi weekly water changes at 25-30% is standard. Also there is little bacteria in the actually water column so a big water change won't kill off bacteria.


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post #11 of 17 (permalink) Old 06-05-2015, 10:51 PM
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I do maybe a 30% water change every week. 50% is really for people who dose ferts or have a large bio load. You can get away with less without causing any issues. I just suggest taking readings before your water change at the one week point and seeing how much nitrate build up you have and work from there.


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post #12 of 17 (permalink) Old 06-05-2015, 11:57 PM
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Quote:
Originally Posted by klibs View Post
lol
Big chain LFS have no clue what they're talking about from what I have seen.
Not really an LFS if it's a chain. I also work at a PetSmart, and let me tell you... people have almost no common sense when it comes to aquarium keeping. I'm talking both new hobbyists as well as employees (even 90% of managers have NO clue what they're talking about). If someone were to come in asking aquarium advice any day I'm not there, I know they will be getting bad advice It's sad, but it's just a job to most people especially ones who are not hobbyists before employment. HENCE the most basic training is given to help try to bridge the gap between no knowledge whatsoever to a very VERY basic understanding. So this is why it is recommended to customers to do AT LEAST a 10% change once a week or a 25% change once a month. The reason for this is to remove nitrates, which as you should know are the last step in the nitrogen cycle; in tanks w/ just fish (like 99% of customers), this is the only way to remove them and keep them from reaching toxic levels. We just dont want people to have massive fish loss w/ new tanks, which unfortunately happens often when associates do not properly guide or inform new aquarium hobbyists. Planted tanks benefit from some nitrate removal via plants.

As has already been stated, we do larger water changes around here for multiple reasons, the biggest probably being:
With EI (estimative index) fertilizing, you essential over-dose your tank to make sure nutrients are available, then by doing your larger water change, you can remove the extra nutrients that aren't being used before algae is able to take off. Water changes do not affect bacteria if done properly, however if too large a change is made so as to greatly change water conditions and shock your fish, then you can have other issues.

It makes me cringe when I hear or see associates other than myself performing water tests for people and telling them their CRAP water is good and add more fish. I intervene when I can, but some people just don't care to learn. It's good advice to take what you hear from chain pet stores w/ a grain of salt, but if you're really lucky you'll get someone who actually does care and has some knowledge (like me ).


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post #13 of 17 (permalink) Old 06-06-2015, 12:45 AM Thread Starter
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Lots of great information!
Thank you everyone for clearing it up for me!

I will be doing a 50% water change tomorrow, my 29 has been running since Monday, I have 0 ammonia but my nitrites and nitrates are slightly high. And my water is still a tad cloudy (I know that's normal for a new tank)
But the few fish I have in there are doing great!
So a 50% wc is still okay to do in a newer tank?
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post #14 of 17 (permalink) Old 06-06-2015, 12:58 AM
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Quote:
Originally Posted by Sarraa View Post
....
So a 50% wc is still okay to do in a newer tank?
Ideal time for big changes.... clean water never hurt a fish

addit - nitrites do hurt fish - if you are noting nitrites, I'd be doing 50% every day.... and add an extra dose of Prime....
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post #15 of 17 (permalink) Old 06-06-2015, 12:59 AM
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Originally Posted by Sarraa View Post
Lots of great information!
Thank you everyone for clearing it up for me!

I will be doing a 50% water change tomorrow, my 29 has been running since Monday, I have 0 ammonia but my nitrites and nitrates are slightly high. And my water is still a tad cloudy (I know that's normal for a new tank)
But the few fish I have in there are doing great!
So a 50% wc is still okay to do in a newer tank?
50% is fine. The 50% water change is a guideline you can do more or less depending on your tank and what you have in. For example my shrimp tanks I do no more than 25% change at a time, my planted tanks I do anywhere from 50-90% weekly.


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