Cascading Water Changes...Dumb Idea?

[grassy_noel]

So, I recently set up a 10 gallon tank next to my 20 gallon mixed reef. Originally the 10 gallon was a QT tank, but it has now served its purpose (I never needed to medicate) and I don't plan on adding any more fish to my 20 gallon. So I'm thinking of converting the small tank into a little softy system with just 1 fish, a couple interesting inverts, and some easy softies.

On the 20 gallon tank, I'm doing I'm providing the best water conditions I can. I'm running a protein skimmer, dosing 2-part, etc. The water is pretty stable at 77-78F, 8.0-8.2 pH, 400-420 ppm Ca, 8.0-8.5 dKH, 1,350-1,450 ppm Mg, 2-5 ppm nitrate, and 0 phosphate (I realize this needs to come up). I change 3 gallons (~15%) of water every weekend.

On the 10 gallon, I'm running a media caddy with chemipure blue and that's about it.

My question is, instead of changing water on both systems, can I change the water on my bigger tank (through a filter sock), and use that waste water as the "new" water for the smaller tank?

I realize the smaller tank wouldn't be getting pristine water, but it would be low in nitrates/phosphates and balanced in terms of Ca/Alk/Mg. It would also be a fairly large change for the small tank (30%+). Since it will be a softy tank, I would think slightly lower quality water wouldn't be the end of the world.

Maybe this is a dumb idea, but if it worked, it would save me from having to mix extra water every weekend, and it would be more "efficient" in terms of salt and labor in the long run.

Just curious.

 

[Billdogg]

IMHO, that will work perfectly. In fact, the soft corals prefer somewhat less than “pristine “ water so they should be very happy there!

Good luck, and post pictures!!!

 

[chipmunkofdoom2]

If the water is "good enough" to be put in the 10g tank, why are you changing it out of the 20 in the first place? Or to put it another way, why is "waste water" from tank A not waste water when put in tank B?

 

[grassy_noel]

If the water is "good enough" to be put in the 10g tank, why are you changing it out of the 20 in the first place? Or to put it another way, why is "waste water" from tank A not waste water when put in tank B?

I think my description and @Billdogg 's response say why.

If we look just at nitrate and phosphate, my target parameters for the mixed reef are 2-5ppm nitrate and 0.03 ppm phosphate (I realize I'm not there yet), but my target parameters for the softy tank are say 10-20ppm nitrate and ~0.10 ppm phosphate. So the "waste water" from Tank A would reduce at least those two nutrients from Tank B.

 

[MaddyP]

So, I recently set up a 10 gallon tank next to my 20 gallon mixed reef. Originally the 10 gallon was a QT tank, but it has now served its purpose (I never needed to medicate) and I don't plan on adding any more fish to my 20 gallon. So I'm thinking of converting the small tank into a little softy system with just 1 fish, a couple interesting inverts, and some easy softies.

On the 20 gallon tank, I'm doing I'm providing the best water conditions I can. I'm running a protein skimmer, dosing 2-part, etc. The water is pretty stable at 77-78F, 8.0-8.2 pH, 400-420 ppm Ca, 8.0-8.5 dKH, 1,350-1,450 ppm Mg, 2-5 ppm nitrate, and 0 phosphate (I realize this needs to come up). I change 3 gallons (~15%) of water every weekend.

On the 10 gallon, I'm running a media caddy with chemipure blue and that's about it.

My question is, instead of changing water on both systems, can I change the water on my bigger tank (through a filter sock), and use that waste water as the "new" water for the smaller tank?

I realize the smaller tank wouldn't be getting pristine water, but it would be low in nitrates/phosphates and balanced in terms of Ca/Alk/Mg. It would also be a fairly large change for the small tank (30%+). Since it will be a softy tank, I would think slightly lower quality water wouldn't be the end of the world.

Maybe this is a dumb idea, but if it worked, it would save me from having to mix extra water every weekend, and it would be more "efficient" in terms of salt and labor in the long run.

Just curious.

Asolutely! I have used this method on several smaller tanks with great success.

 

[chipmunkofdoom2]

I think my description and @Billdogg 's response say why.

If we look just at nitrate and phosphate, my target parameters for the mixed reef are 2-5ppm nitrate and 0.03 ppm phosphate (I realize I'm not there yet), but my target parameters for the softy tank are say 10-20ppm nitrate and ~0.10 ppm phosphate. So the "waste water" from Tank A would reduce at least those two nutrients from Tank B.

I don't think that's a good reason to do what you're describing. If the water you're taking out of your 20g is good enough for another tank, except for the nutrients, reduce the nutrients and leave the water in the 20g. Changing water to reduce nutrients is not an effective long-term strategy. If you want to maintain low nutrients in a tank (which may not even be a good idea), do so by using algae, organic carbon, or some other method like a phosphate binder. The foods that we feed contain far too much N and P for water changes to be a sensible comprehensive nutrient management strategy, especially at the levels you quote.

 

[MaddyP]

Changing water to reduce nutrients is not an effective long-term strategy.

Unless I'm missing something, the entire point behind water changes is to reduce nutrients by means of exporting said nutrients. Yes, there are other methods of controlling nutrients in addition to or in absence of water changes. But to say water changes are not an effective long-term strategy for controlling nutrient levels is misleading.

Personally, I have used this method of transferring "old" water from larger tanks to smaller tanks with success. Nutrients can be managed properly in this type of way, so long as other husbandry needs are met.

 

[grassy_noel]

I don't think that's a good reason to do what you're describing. If the water you're taking out of your 20g is good enough for another tank, except for the nutrients, reduce the nutrients and leave the water in the 20g. Changing water to reduce nutrients is not an effective long-term strategy. If you want to maintain low nutrients in a tank (which may not even be a good idea), do so by using algae, organic carbon, or some other method like a phosphate binder. The foods that we feed contain far too much N and P for water changes to be a sensible comprehensive nutrient management strategy, especially at the levels you quote.

That is a fair point. I have often thought that since i'm only changing ~15% of my water a week, that it could not be a long-term sustainable strategy for maintaining desired levels of nitrate and phosphate. I guess it's ultimately a function of the NET amount of each nutrient added in a week. By NET, I mean the amount added in food minus the amount bound by algae, corals, fish, and inverts, or removed otherwise (protein skimmer?).

If from feeding, NET 1 ppm of nitrate is added per week, and the level of nitrate in the tank at the end of the week was 7 ppm, then a 15% water change would reduce it to ~6 ppm, and over the course of the week it would increase back up 1 ppm to ~7 ppm. Rinse, repeat, equilibrium!

So, in that case, it all depends on how much NET nitrate, phosphate, etc. is being added each week and how much water you change that determines the ultimate equilibrium concentration of each nutrient.

 

[chipmunkofdoom2]

Unless I'm missing something, the entire point behind water changes is to reduce nutrients by means of exporting said nutrients. Yes, there are other methods of controlling nutrients in addition to or in absence of water changes. But to say water changes are not an effective long-term strategy for controlling nutrient levels is misleading.

Personally, I have used this method of transferring "old" water from larger tanks to smaller tanks with success. Nutrients can be managed properly in this type of way, so long as other husbandry needs are met.

This single sentence you quoted out of my post is missing context and does not completely express the point I was trying to make. At the end of my post, I stated my point much more clearly. Water changes are not sensible (efficient) comprehensive nutrient management strategy (read: the only way you control nutrients), especially at the levels you quote (30 ppb phosphate and 3-5 ppm nitrate).

Nowhere did I say what @grassy_noel is proposing couldn't or wouldn't work. I'm saying that I personally wouldn't do it because it's expensive, wastes a lot of water, and takes a lot of time.

 

[chipmunkofdoom2]

That is a fair point. I have often thought that since i'm only changing ~15% of my water a week, that it could not be a long-term sustainable strategy for maintaining desired levels of nitrate and phosphate. I guess it's ultimately a function of the NET amount of each nutrient added in a week. By NET, I mean the amount added in food minus the amount bound by algae, corals, fish, and inverts, or removed otherwise (protein skimmer?).

If from feeding, NET 1 ppm of nitrate is added per week, and the level of nitrate in the tank at the end of the week was 7 ppm, then a 15% water change would reduce it to ~6 ppm, and over the course of the week it would increase back up 1 ppm to ~7 ppm. Rinse, repeat, equilibrium!

So, in that case, it all depends on how much NET nitrate, phosphate, etc. is being added each week and how much water you change that determines the ultimate equilibrium concentration of each nutrient.

Those considerations are valid for nitrates, but phosphate are likely to be a bigger issue, especially because they're present in relatively high concentrations in foods:

Flake fish food is typically about 1% phosphorus (3% phosphate equivalent) by weight (and many products have such phosphorus data on their labels). Consequently, if five grams of flake food is added to a 100-gallon aquarium, there is the potential for the inorganic orthophosphate level to be raised by 0.4 ppm in that SINGLE FEEDING!

Additional, the animals we keep don't really use much of the phosphates in foods, and most of it gets excreted back into the water:

A fish, whether it is an adult or a growing juvenile, consequently excretes much of the phosphorus that it takes in with its food as phosphate in its waste. Of course, overfeeding will result in more phosphate delivery than will reduced feeding levels.

What you're describing certainly won't harm any of the animals in your care, but I don't think it's the most efficient way to achieve your goals. Maintaining phosphate levels in the tens of parts per billion is going to be challenging with water changes alone. I would personally not choose to go this route, but, to each his own.

 

[grassy_noel]

I appreciate the recommendation, and that math on phosphates checks out...it's pretty shocking!

I wonder how much phosphate the photosynthetic algae in our tanks soak up, and whether a healthy stocking of corals and coralline algae make any significant difference? We know that macroalgae (in relatively large quantities) can certainly soak up a meaningful amount of phosphate...

I tend to agree with you, and am probably just looking for a shortcut, but as you state there's probably no harm in trying. If it doesn't work, I can always add another nutrient export method.

 

[Art2249]

I think water changes are a good idea just because of things we may not be testing for or even aware of. Small frequent water changes. As far as nutrients go only one of my 3 tanks can have a refugium. I actually have to add phosphate to my small tanks to keep it above 0.