AWC - fast or slow?

[tb582]

My nitrates in my tank that’s about 6mo old are around 10-15ppm … I have my dos that does water change 3gal everyday so per week it’s about 28% of the water that’s getting refreshed.

To drive the nitrate numbers down do I need to change more water per day?

 

[Waters]

My nitrates in my tank that’s about 6mo old are around 10-15ppm … I have my dos that does water change 3gal everyday so per week it’s about 28% of the water that’s getting refreshed.

To drive the nitrate numbers down do I need to change more water per day?

First off, I think your nitrate numbers are fine unless you are seeing issues? Secondly, yes, if you want to remove more nitrates faster, you can do larger or more frequent water changes.

 

[cwerner]

User above is correct, but please note that this is a pretty inefficient and expensive method of removing nutrients, though there's definitely nothing wrong with daily AWC. You'll go through a lot of saltwater that way. Something like BioPellets/Algae Reactor/Scrubber/Refugium paired with a skimmer is much more efficient and doesn't require large volume replacement. By definition unless you're doing a 100% water change there WILL be nutrients accumulating in the tank. It's probably just kept up with by your existing skimmer or other nutrient export methods.

 

[tb582]

First off, I think your nitrate numbers are fine unless you are seeing issues? Secondly, yes, if you want to remove more nitrates faster, you can do larger or more frequent water changes

User above is correct, but please note that this is a pretty inefficient and expensive method of removing nutrients, though there's definitely nothing wrong with daily AWC. You'll go through a lot of saltwater that way. Something like BioPellets/Algae Reactor/Scrubber/Refugium paired with a skimmer is much more efficient and doesn't require large volume replacement. By definition unless you're doing a 100% water change there WILL be nutrients accumulating in the tank. It's probably just kept up with by your existing skimmer or other nutrient export methods.

I should clarify I don't have a sump ... I'm new to this hobby so the tank was first lol.

I guess I need to determine if the 28% water change per week is too much, I think I've heard it should be around 10% per week so maybe I should dial it back a bit ?

 

[Waters]

I should clarify I don't have a sump ... I'm new to this hobby so the tank was first lol.

I guess I need to determine if the 28% water change per week is too much, I think I've heard it should be around 10% per week so maybe I should dial it back a bit ?

Your water change frequency (and amounts) are dictated by your nutrient levels. Technically you can change as much water at a time as you want as long as the chemistry matches up. There are people that change close to 100% of their water at one time in smaller nano tanks. The 10% per week is an outdated number. I do aggressive water changes and change roughly 15 gallons via AWC and another 15 through manual changes once a week in a 105 gallon system which averages out closer to 30% a week. This keeps my nitrates around 8-10 and phosphates about .08 with consistent feedings, while replenishing anything that is lost.

 

[cwerner]

I should clarify I don't have a sump ... I'm new to this hobby so the tank was first lol.

I guess I need to determine if the 28% water change per week is too much, I think I've heard it should be around 10% per week so maybe I should dial it back a bit ?

It's not going to hurt anything, it's all about what you're willing to spend on saltwater when it's not providing a tangible benefit exactly. Your nutrients will likely continue to slowly climb unless you have some other sort of export method. While water changes do remove nutrients they are best for removing other things that slowly build up. It's quite possible that you're able to keep up with your nutrient generation by doing the 10% weekly method + whatever other forms of export that you have.

 

[thatmanMIKEson]

awc's will more than likely be removing some of the new water unless your removing the total amount first, then replacing the total amount. if both are happening simultaneously I don't see how it can be counted as a percentage accurately.

 

[TokenReefer]

At face value - Fast makes more sense (in my mind) if the goal is dilution fwiw

 

[Waters]

awc's will more than likely be removing some of the new water unless your removing the total amount first, then replacing the total amount. if both are happening simultaneously I don't see how it can be counted as a percentage accurately.

It was actually tested (can't remember by who....BRS maybe?) that the amount of new water that would be removed is minimal. Wouldn't be enough to throw off any measurements of percentage of water changed. It is required to prevent the ATO from triggering.

 

[TokenReefer]

I agree with @thatmanMIKEson. Although I suppose you could consider different levels of automation. I wouldn't mind shutting things off as if I was doing a manual wc but having a unit do it for me. I don't think they're quick enough tho for my vision...

 

[thatmanMIKEson]

It was actually tested (can't remember by who....BRS maybe?) that the amount of new water that would be removed is minimal. Wouldn't be enough to throw off any measurements of percentage of water changed. It is required to prevent the ATO from triggering.

thats fine but remember BRS sells everything involved in the hobby.

even if it's minimal, everything adds up. every system is different, so it would be hard for them to do a test that would be accurate information for everyone. The way one person sets it up may be much different than how I set it up wasting more water, multiply that over a year it may add up to alot of wasted water and if it's being done to lower or maintain something for some reason, it's working against itself in some way.

you could have your ato on a controller that shuts off the ato at the time of the awc, have the entire amount removed first, then replaced.

I dont see awc's being as effective as large manual waterchanges, in the way most people implicate them, but every system is different so I'm sure some people have it set up very well too.

 

[Waters]

thats fine but remember BRS sells everything involved in the hobby.

even if it's minimal, everything adds up. every system is different, so it would be hard for them to do a test that would be accurate information for everyone. The way one person sets it up may be much different than how I set it up wasting more water, multiply that over a year it may add up to alot of wasted water and if it's being done to lower or maintain something for some reason, it's working against itself in some way.

you could have your ato on a controller that shuts off the ato at the time of the awc, have the entire amount removed first, then replaced.

I dont see awc's being as effective as large manual waterchanges, in the way most people implicate them, but every system is different so I'm sure some people have it set up very well too.

This was done years ago...way before BRS sold out lol. I do agree that it would be difficult to an accurate test, but if you are pulling water from one section of your sump, and returning it to the return section as it is being mixed in with 100+ gallons, the chance of removing any substantial amount of duplicate water is pretty minimal. Also remember that large, manual water changes have the potential of throwing off water chemistry while slow weekly AWCs help to keep everything stable, which is what we are trying to achieve. Don't get me wrong, I do both.....but my tank has improved greatly since I started doing AWCs. There are times where large manual water changes are not only better but required (such as removing harmful substances quickly) but for normal weekly water changes you can't beat AWCs.

 

[glb]

I have a DOS. If you put the tubing to remove the saltwater behind the flow of the tubing with new saltwater, you won’t pull out the new water. My dos pulls water out of the skimmer section and the new water goes in where the return pump is.

For nutrient removal, a good skimmer really helps.

 

[Randy Holmes-Farley]

awc's will more than likely be removing some of the new water unless your removing the total amount first, then replacing the total amount. if both are happening simultaneously I don't see how it can be counted as a percentage accurately.

It can, if you know how you are doing it. The effect is minor.

Water Changes in Reef Aquaria by Randy Holmes-Farley - Reefkeeping.com

Size of Water Changes: A General Case
As shown in the previous section, a fixed number of small water changes is not as beneficial as the same fixed number of larger water changes. However, for an aquarist who wants to do water changes, the decision of how to change the water should not be driven by that analysis alone. The conclusion of such an analysis is different if one assumes that the aquarist has a fixed volume of water to change, and is just deciding how to accomplish it.

For example, with a 100-gallon tank and a goal of changing 30 gallons each month, one might consider changing 30 gallons once, 15 gallons twice, 10 gallons three times, 5 gallons six times or 1 gallon 30 times. In the extreme case, we can imagine changing an infinitesimally small amount of water an infinitely large number of times, eventually consuming the entire 30 gallons (I actually do this in my aquarium, as I'll explain).

Aquarists often think that many small changes are not as efficient as one big change since some of the water in all subsequent changes was already replaced by earlier changes. This is a correct assertion, but it is often overstressed. After changing 10% three times, only 10% of the first 10% change was changed the second time (1% of the total). So the difference is small. We can mathematically calculate the efficiency of such changes as follows. If we use our 30% example, then one 30% change removes 30% of the impurities, assuming an equal distribution of the impurity within the water. If we do six 5% changes, then the reduction in impurities = 1-(0.95)6 = 26.5%. So it is less efficient (six 5% changes exactly equal 26.5% changed in one batch), but it is not radically less efficient. Going smaller still, the difference is even smaller. Doing 30 one percent changes removes 1-(0.99)30 = 26.0% of the impurities.

The extreme case of infinitely small water changes done an infinitely large number of times is approximated by continuous water changes that add water at exactly the same rate it is being removed. The details of how to do this mechanically are described below. This case is a standard example in advanced math textbooks (differential equations, specifically). Assuming the aquarium is well-mixed as the water is changed, the remaining impurities are given by:

I = Ioe(-C/T)

where I is the amount of impurities present, Io is the amount present at time zero, e is the constant 2.71828, C is the amount changed, and T is the tank's total volume. So for 30 gallons changed this way in a 100-gallon tank, the remaining impurity is 0.74 times Io, or a reduction of 25.92%.

The table below compares these results for a 30% water change done via different numbers of smaller changes. Clearly, the single 30% change is a little better than the others (70% vs. 72-74% initial impurities remaining), but the difference is quite small, and the difference between the others in efficiency is trivial.

 

[Randy Holmes-Farley]

It was actually tested (can't remember by who....BRS maybe?) that the amount of new water that would be removed is minimal. Wouldn't be enough to throw off any measurements of percentage of water changed. It is required to prevent the ATO from triggering.

I modeled it before BRS existed.

 

[Dburr1014]

OP, I have a question....or two.

Are you using rodi? Are you on a well?
Zero TDS is ideal and if your not, are you adding no3 inadvertently?

 

[dangles]

I'm new as well so take this with a grain of salt...

Your "higher" nutrient levels (they're not terribly high) most likely come from the amount of food you put in, and not having a good nutrient export option. Yes, you COULD do bigger water changes. You mentioned not having a sump so I assume you're using a traditional aquarium? Or an AIO? Either way a couple of other options are to get a HOB refugium, and/or a HOB skimmer. Or feed a little less

I do 2% WC per day using a DOS set up for AWC, but I also do a manual WC of about 10% each week when I siphon out the sandbed. I added a refugium to my AIO and that has REALLY done a good job of getting my nutrients into range.