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

[Calihawk]

If only most people who keep aquariums did EITHER one 50% water change per week...or two 25% ones! I'd guess that 90% do not....probably even monthly.

If you're going to do two 25% water changes per week, why not just make one of them 40-50%? A few minutes extra but worth it.

Also, I'm a fan of mixing in a large (75%) water change every month or so to reduce nitrate and other waste in the tank to near the levels from the tap.

Matt

OMG, once a month??? No WAY for my tank

 

[vfc]

Here is the same bio-load with a 90% WC once a month.

 

[Rayne]

Do you have a link where this spreadsheet is hosted online? Or did you create it yourself?

 

[calioutlaw1a]

Your theory/argument/reasoning is wrong. I'm not even bother with data, and number, and just go with common sense and nature observation. While you're focus on the small picture of nitrate level, you're missing the big picture of mineral depletion, pH level, and hormone released by fish in to aquarium water. Thus, small amount of water change at more often frequency is better than large amount of water change at less frequency. Look at nature. Fish lives in river, stream, where water flows constantly from high ground to lower ground. At any location, you have constantly/frequently water change, supply by cleaner water from high ground that flows thru that point. In summary, a 50% weekly water change won't be better than two 25% water change per week.

This is exactly why I made this post, because many would agree with you without looking at the actual numbers. The same principle applies to the amount of minerals and hormones. With a 50%wc you are actually increasing the average mineral content and decreasing the average hormone concentration per week.

25% every 3 days is better than 50% per week given your bio-load parameter (20PPMs/week or ~3PPMs/day). The nitrate swings are less severe.

Of course the nitrate swings are greater with 50%wc, that is the whole point. A 50%wc per week reduces nitrates more than two 25%wcs per week.
If you are suggesting that fluctuating nitrate levels is harmful to fish, what evidence or logic supports this conclusion? Again, when talking about parameters like temperature or total dissolved solids there is plenty of evidence to show that large swings are detrimental. But we are talking about reducing a toxin each week. Essentially you are saying it is better to maintain a toxin at a higher level rather than reduce it to a greater extent each week.

I think that it is hard to pinpoint a percentage that will be optimal for every tank. A very lightly stocked tank can probably be fine with 25% per week or less, while a heavily stocked tank might need well over 50% per week in water changes. In my view a constant-flow water change is better than weekly or bi-weekly changes, it keeps water parameters nice and stable.

I completely agree. My post is directed at those who do multiple smaller water changes per week rather than a single larger water change.

Ive got a High bioload and my tank still sets fine at a 25% biweekly. I think every tank is different and you just have to find what works for you. But great info on this forum!

I agree that every tank is different and we all have different lifestyles and different approaches to the hobby. I'm definitely not going to ask anyone to make drastic changes based on the data I gave, but this is actually less work to do one large wc per week, and nitrates are actually lower. May I ask why you do biweekly 25%wcs?

 

[jlnguyen74]

This is exactly why I made this post, because many would agree with you without looking at the actual numbers. The same principle applies to the amount of minerals and hormones. With a 50%wc you are actually increasing the average mineral content and decreasing the average hormone concentration per week.

Would it be better to increase the mineral content and decrease the hormone concentration twice a week, or once a week? Use your own body as an example. Would it be better to drink a glass of water and go to the bathroom twice a day, or would it be better to drink two glasses of water and go to the bathroom only once a day?

 

[jlnguyen74]

Of course the nitrate swings are greater with 50%wc, that is the whole point. A 50%wc per week reduces nitrates more than two 25%wcs per week.
If you are suggesting that fluctuating nitrate levels is harmful to fish, what evidence or logic supports this conclusion? Again, when talking about parameters like temperature or total dissolved solids there is plenty of evidence to show that large swings are detrimental. But we are talking about reducing a toxin each week. Essentially you are saying it is better to maintain a toxin at a higher level rather than reduce it to a greater extent each week.

Like I said, you're missing the big picture. Instead of a fish living with "x" amount of nitrate every 3.5 days with 25% water change twice a week, it will lives with "2x" amount of nitrate every 7 days with 50% weekly water change. It's not the fluctuating nitrate is harmful to fish. It's living with nitrate for longer period is harmful to fish.

 

[jcardona1]

Funniest thing in the world. I told my buddy hey if you wnt to get rid of your fish Post on this site. He calls me back and says I signed up for the site and Coulnt find where to post for the life of me.... So i said You idiot Give me the info ill post it. Sure enough I got to the site And Lo and behold this is the only site i have ever seen without the words POST HERE... So We went elsewhere but just to share this with the idiot who designed the site that there are idiots like me who probably pass this site up for the simple fact its not simple. Get a clueif you want more revenue. Keep it Simple Stupid Give me a POST HERE button.... A CLICK HERE TO POST!.... you know the things we look for that make a site great!!!! And keep it on a 6th grade level. This is more like a cult where you have to have a friend that knows to know...!

I find it hard to believe that two normal adults with average intelligence couldn't figure out how to use a forum. You must really have a hard time with life in general, if you're so ignorant.

 

[vfc]

..."You cannot polish a turd"...

Actually you can.....lol.

 

[jcardona1]

On my 190g discus tank, I change 40g (about 20%) via a semi-automatic setup, either daily or every other day. Nitrates are 0ppm.

 

[jcardona1]

If you are suggesting that fluctuating nitrate levels is harmful to fish, what evidence or logic supports this conclusion? Again, when talking about parameters like temperature or total dissolved solids there is plenty of evidence to show that large swings are detrimental. But we are talking about reducing a toxin each week. Essentially you are saying it is better to maintain a toxin at a higher level rather than reduce it to a greater extent each week.

I agree on this point. I don't know where this notion came from; that swinging nitrate levels are bad for fish. Is there any evidence to support that? Other parameters like TDS and PH, yes. But that's an invalid argument since we're already doing constant water changes. Parameters between the tap and the tank will be similar, if not identical, and you could theoretically do a 100% water change with no ill effects on the fish.