Why a weekly 50% WC is better than two weekly 25% WCs

[Poloboy]

i do 2 times a week a wc of 25% to keep my water values the same

i do this because i have a tight schedule with work

 

[ScatMan]

i do 2 times a week a wc of 25% to keep my water values the same

the water you put in should have almost the same "values" as the water you take out ( - nitrates).

doing 25% 2x a week vs 50% 1x a week is a waste of time fyi; unless you have an enormous tank that takes too long to empty and fill in one session. for me, setting up and putting away wc equipment takes more time and breaks more balls than draining and refilling.

 

[Poloboy]

the water you put in should have almost the same "values" as the water you take out ( - nitrates).

doing 25% 2x a week vs 50% 1x a week is a waste of time fyi; unless you have an enormous tank that takes too long to empty and fill in one session. for me, setting up and putting away wc equipment takes more time and breaks more balls than draining and refilling.

there you have a good point, i'm going to do it like you said, its always a big time thats past before i got the equipment out.

 

[jcardona1]

doing 25% 2x a week vs 50% 1x a week is a waste of time fyi

Like I mentioned in my post above, if it fits in your schedule and lifestyle, who cares, it's all the same. When looking the effective percentages of water changed over a period of time, the difference is so miniscule, it's silly to claim one method is "better" than the other.

 

[ScatMan]

Like I mentioned in my post above, if it fits in your schedule and lifestyle, who cares, it's all the same. When looking the effective percentages of water changed over a period of time, the difference is so miniscule, it's silly to claim one method is "better" than the other.

not really. you definitely have a lower average nitrates with the bigger wc (even thought the difference is not huge) and it saves time and energy of setting/cleaning up wc equipment twice rather than once.

25% 2x a week would only be beneficial in the incredibly rare circumstance that you don't have enough time to drain and refill 50% of your water vs 25%. i've never met or heard of anyone shaving their time so thin (not saying they don't exist, just never heard of it).

 

[jcardona1]

you definitely have a lower average nitrates with the bigger wc

You can't really say "definitely" either, when there is such a small difference in the amount of water effectively changed over a period of time. Maybe there is, maybe there isn't. Only way to really know is to set up a controlled test environment, and measure nitrates with an lab-grade digital monitor (not a liquid test kit) everyday for several weeks. You would need the fish to consume the same amount of food and produce the same amount of wastes to even make the experiment accurate, which would be very difficult to do.

I don't do one large weekly water change because I'm using RO water, and I would need several barrels to store enough water for a weekly 50-60% water change. That doesn't work for me, so I do smaller water changes more frequently. And the way I set my system up, it's a breeze. All I do is push two buttons on a remote, one to drain, and one to refill. Not everybody's tank and setup is the same, so you can't make a blanket statement like that.

You don't know exactly how much waste your fish will produce in a day or a week. Sometimes you may feed them less, or more. Or some days they won't eat as much, or they may eat more, causing differences in waste produced. So you really can't use nitrates as a constant in the formula. The only thing you really can look at is the effective water changed over a period of time, since that is easy to calculate. And based on the effective water changed calculation, the difference is too small to say without a doubt that a weekly 50% water change is "better".

 

[jlnguyen74]

Thanks Scatman for helping me out here. I didn't realize this would be so difficult.

In these scenarios there is the same amount of water removed (50%) over the same amount of time (1 week).
So to answer your question: I would rather relieve 50% of the volume in my bladder and have it fill back up over the course of the week so I only need to pee for the last half of the week, rather than relieving 25% of the volume in my bladder twice in the week which would feel full throughout the whole week.

You got it backward. For the 50% weekly, your bladder get relieved once a week, and when it's filled back up, you have to wait the entire week until it get relieved again. For 25% twice a week, you bladder get relieved every 3.5 days. Is it really that difficult? I can make it's easier for you.. Do you think it's better if you drink two bottles of water when you wake up, and hold it the whole day, go to bed, and wake up the next day to relieve it then drink another two bottles of water and go thru the same routine? Or would you rather drink a bottle of water when you wake up, relieve it in the evening, drink another bottle of water, go to bed, wake up, relieve it in the morning, then drink a bottle of water and go thru that same routine?

No. With a 50%wc, the nitrate is reduced to 20ppm whereas with each 25%wc the nitrates are only reduced to 30ppm. The fish are exposed to LESS nitrates with one 50%wc. The numbers don't lie.

You're right. The numbers don't lie, but you didn't see that the fish in 50% weekly wc situation exposed to nitrate level of 40ppm, before the water was changed to drop it, while it doesn't happen to 25% wc twice a week

 

[ScatMan]

You can't really say "definitely" either, when there is such a small difference in the amount of water effectively changed over a period of time. Maybe there is, maybe there isn't. Only way to really know is to set up a controlled test environment, and measure nitrates with an lab-grade digital monitor (not a liquid test kit) everyday for several weeks. You would need the fish to consume the same amount of food and produce the same amount of wastes to even make the experiment accurate, which would be very difficult to do.

it doesn't matter the level of waste in the system, you can replace 20ppm per week with 1,000,000ppm and you'll get the same results: larger wc gives you lower average of ppm no matter how you slice it.

you could "in theory" flip a coin 1,000 times and it land on heads every time, but odds are it will land on heads 50% of the time or damn near close to it and experiments have proven this fact.

I don't do one large weekly water change because I'm using RO water, and I would need several barrels to store enough water for a weekly 50-60% water change. That doesn't work for me, so I do smaller water changes more frequently. And the way I set my system up, it's a breeze. All I do is push two buttons on a remote, one to drain, and one to refill. Not everybody's tank and setup is the same, so you can't make a blanket statement like that.

that's good for you. it doesn't change the fact that one large water change would lower (albeit slightly lower) your average nitrate concentrations or that you are pushing the button twice as much (albeit slightly more work). this is not a matter of opinion.

You don't know exactly how much waste your fish will produce in a day or a week. Sometimes you may feed them less, or more. Or some days they won't eat as much, or they may eat more, causing differences in waste produced. So you really can't use nitrates as a constant in the formula. The only thing you really can look at is the effective water changed over a period of time, since that is easy to calculate. And based on the effective water changed calculation, the difference is too small to say without a doubt that a weekly 50% water change is "better".

now that's an opinion. #'s don't lie. if you don't think the (very real but small) difference is enough to matter to you, that's one thing, but that doesn't mean it doesn't matter to everyone else. that would be a true "blanket statement".

again, it doesn't matter the level of waste in the system, you can replace 20ppm per week with 1,000,000ppm and you'll get the same results: larger wc gives you lower average of ppm no matter how you slice it.

 

[ScatMan]

You're right. The numbers don't lie, but you didn't see that the fish in 50% weekly wc situation exposed to nitrate level of 40ppm, before the water was changed to drop it, while it doesn't happen to 25% wc twice a week

yes it does, look at the math again. ppm will max out at 40 in both examples.

 

[jcardona1]

again, it doesn't matter the level of waste in the system, you can replace 20ppm per week with 1,000,000ppm and you'll get the same results: larger wc gives you lower average of ppm no matter how you slice it.

I understand all that fully. But what I'm saying is, regardless of nitrates, the difference in changing you water weekly vs biweekly after one month is 3.76% (3.76% more water changed when it's done weekly). Whether it be a 10g tank or a 1000g tank, that percentage is still the same.

Is 3.76% of a tank's volume over a one month period enough to make a discernible difference in nitrate levels that's worth debating over? I'm almost certain the answer is no. Take for example a 300g tank, that's 11 gallons of water. How much of an effect on nitrates you think you're going to have if you change 11g of water?