What's better 50% wc or 25%x2 per week

  • We are currently upgrading MFK. thanks! -neo
25% twice a week. It simply is less of a change at once and is easier for sensitive species to handle.

You also want to do WC that frequently for alot of reasons. It removes the waste, hormones etc (everything already mentioned). Yes your anaerobic bacteria and plants can remove some waste, but its a find balancing act. If your plants are not flourishing, they are not effectively removing waste. Bacteria and plants can only remove so much. Hardness and pH are other factors that your filter will not control. Depending on substrate and decor, this could be a big issue. Then it depends on how much you feed, your bio load and what species.

I perform 10% daily AND 60% weekly and I still dont think my tanks are clean. I blame the plecos, Its hilarious how "cleaner" fish produce the most waste
 
i do 20-30% in all my tanks every week. I might increse wcs a little when my smaller fish get larger but my fish are healthy, happy , health and have clean water for now...
 
target ppm (T) 140
ppm/day added (P) 5
amount changed (C) 25%

days to next change 7


This is how I model my water changes. I'm not validating the math, so someone else can correct this if they see a flaw.

T=target highest level of toxins allowed in the system
P=amount of poisonous toxins added each day to the system
C=% of water removed and replaced with clean toxin free water

The formula is T/P*C=days to change

For example, if you change 25% every 7 days and you add 5PPM of nitrates per day, your stable long term system will be level at 140 PPM. That is after a long running time (many weeks), the typical condition will be a tank that has 140 PPM of nitrates before a water change and 105 ppm after a water change.


Below is the comparison of the 25% x2 or the 50% x1 example.

target ppm (T) 70
ppm/day added (P) 5
amount changed (C) 50%

days to next change 7
This tracks daily readings as 70--->35, 40, 45, 50, 55, 60, 65, and 70. ("----->" is the symbol for a water change.)

target ppm (T) 70
ppm/day added (P) 5
amount changed (C) 25%

days to next change 3.5
This tracks daily readings as 70--->52.5, 57.5, 62.5, 67.5, 70.0--->52.5, 57.5, 62.5, 67.5 and 70.


All other things being equal, over the long run, a 50% water change will lower the target to half the level in the same way that doing a 25% change 2 times per week will lower it. Over a short period of time, this is not exactly correct if the tank is operating above or below it's level rate. (E.g., if feeding has been excessive and parameters are higher than T, a single 50% change will be more effective than 2 25% changes each week. But that's not the correct answer if the system is at T.)

Note that this assumes that the changes are done at exactly the same cycles. Doing two 25% water changes one after the other is not the same as one 50% water change each week or one 25% water change every 3.5 days.


Doing two 25% changes each week week may be less stressful on the fish than one 50% change depending on the fish. The same can be said for the effect on the fish keeper. Chemically, I don't think they are different in the long run, provided that T is set to the minimum level that does not affect the fish. Note that the 25% change does have a slightly higher average rate than the 50% change. This is not a problem as long as it's still below the minimum level.

By the same token, we are only discussing water changes. If we include substrate cleaning in the equation, doing it twice a week at 25% might be more effective in the long run. This is however, fairly complex to model.
 
dogofwar said:
25% twice per week creates greater stability...but one 50% water change removes more waste.

If x0 = the initial amount of waste (nitrate) in the tank (mg) and
z= the amount of waste (nitrate) produced per day (mg/day) - assuming constant waste production, and
x7 @ 50% = the amount of waste (nitrate) in the tank after one week in mg

x7 @ 50% = x0 + 7z - .5x0 - .5*7*z
x7 @ 50% = .5x0 + 3.5z

For two 25% water changes per week (on day 3 and day 7):

x3 @ 25% = the amount of waste in the tank (nitrate, mg) after 25% water change on day 3
x3,7 @ 25% = the amount of waste in the tank (nitrate, mg) after 25% waste change on day 7

x3 @ 25% = x0 + 3z - .25x0 - 3*.25z
x3 @ 25% = x0 + 2.25z

x3,7 @ 25% = x3 @ 25% + 4z - .25 * x3 @ 25% - 4 * .25z
x3,7 @ 25% = .5625x0 + 4.6875z

Which is larger (x7 @ 50% or x3,7 @ 25%)?

Assuming x0 = 0, at any rate of waste (nitrate) production, x 3,7 @ 25% is going to have more waste (nitrate) on day 7.

Maybe my math's messed up but makes sense to me :)

Matt
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LOL I love that. LOL my little bro goes to collage and take all types of philosophy classes. And math classes. We cant have a normal conversation without x y and z formulas being used. LOL not mocking or poking fun. You just reminded me of my little brother. LOL is your real name Dustin?

My best friend turned me onto 50% water changes. And others on mfk did the same. Get yourself a bottle of water. Open it and leave it out for a week. Then at the end of the week. Take a sip of the open water bottle and a sip of a new bottle water. I learned about how water ages. Even pool or Jacuzzi water you swim and sit in goes bad. Ive heard ppl tell me that the fish can even grow faster and enjoy fresh water more then the old water they have swam, ate, and pooped in. Makes sence to me.

I think my fish would rather me bother there home once a week. And have 50% fresh water. Than me bugging them 2 or 3 times a week.

Just a opinion from my own questions I have asked in the past.

Doing something is better then the ppl doinf nothing. Good job researching and asming questions. Only dumb mistakes. Come from ppl afraid of asking questions.

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I do 33% every second day. That's 99% a week. Maybe I over do it but I like to keep it safe.
 
Z Trip said:
I do 33% every second day. That's 99% a week. Maybe I over do it but I like to keep it safe.
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defenitly overkill. Well if it keeps your fish happ[y and healthy go for it... I think 2 50%s a week would also be an option...
 
oscaroo said:
defenitly overkill. Well if it keeps your fish happ[y and healthy go for it... I think 2 50%s a week would also be an option...
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Not necessarily over-kill depending on species and bio-load...

I mean some discus keepers are known to do daily 100% water changes...


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I do like 60-80% in one sitting, weekly. Never had a problem. Pumped appropriate temperature tap water right in, add a couple capfulls of prime, and it's golden.

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Mount_Prion said:
I do like 60-80% in one sitting, weekly. Never had a problem. Pumped appropriate temperature tap water right in, add a couple capfulls of prime, and it's golden.

Sent from my Galaxy Nexus using MonsterAquariaNetwork App
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Oh ya! :D id do 90% wc. So there LOL :p

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