'Drip' Water Changes?

[cchardwick]

Yea, that's exactly what I'm talking about. Can you post some photos with details of your peristaltic pump setup? I would really like to see it.

[adeebm]

If say, you have 100ppm nitrates, and you change 50% of the water, you will have 50ppm nitrates left. Now say you change 25%, add new water, and change 25% again. You are then left with 56ppm nitrates. If you do three 15% water changes, you are left with 61ppm nitrates, and so on. So if you are running a continuous water change system, where you add and remove a few drops at a time, imagine how ineffective it would be towards removing nitrates.

 

--Adeeb

[cchardwick]

Yes, much less effective, but just imagine doing a 100% water change on your system in one day the old fashioned way, the shock would kill everything, and if you decided to drastically change your water parameters, say from a salinity of 1.025 to 1.021, you could easily do it with a drip system, just set it up and leave it. With a continual drip system you will never have to suspect your water change or the fresh water top off when things go bad, and you would always know your pH is dead on. And really it would do the same thing a skimmer is doing, since I don't have a skimmer, but instead of just removing organics it would be replenishing everything (buffers, trace elements, calcium, etc..). I'm actually considering a gravity drip system with an overflow drain. I'm thinking a custom black acrylic reservoir behind and just above the tank, maybe something that will hold 2.5 gallons which is 50% of my nanocube water volume.

 

 

 

 

 

If say, you have 100ppm nitrates, and you change 50% of the water, you will have 50ppm nitrates left. Now say you change 25%, add new water, and change 25% again. You are then left with 56ppm nitrates. If you do three 15% water changes, you are left with 61ppm nitrates, and so on. So if you are running a continuous water change system, where you add and remove a few drops at a time, imagine how ineffective it would be towards removing nitrates.

 

--Adeeb

[dubbly]

Writing on a tablet so no spell check... sorry:

 

I run a continous water change on my system. It isn't really that inefficent. In fact in many ways it is more efficent.

 

The following table shows the difference in efficency. If I were to conduct a 50% water change in 1 step I will reduce my Nitrates by 50%. Instead, if I do it in two steps i will reduce reduced the nitrates by ~44%. My continious system will transfer 50% of the water in 1000 or even 10000 steps. This equates a ~40% reduction in nitrates compared to 50% (See table). For this reduced efficency I no longer have to worry about tempature, perfect salinity matching, or me getting lazy. All I do is dump water. In fact, this system is better when, something dies during the week becaue my system is alwasy pulling nitrates! It doesn't wait for me to manually change it.

 

# Steps % Reduction

1 50.0%

2 43.8%

3 42.2%

4 41.4%

5 41.0%

10 40.2%

100 39.5%

1000 39.4%

10000 39.3%

 

Now, with this said this system works great if your stable or if something normal dies. If you have a big event that really poisons your tank then you will want to conduct a manual change. but this is the case either way.

 

just my 2 cents.

 

oh... writing from a tablet no spellchecker.

[mmcguffi]

Can you give us some details on how you have it set up to do continuous WCs?

[cchardwick]

That's some great info. Another thing, if you have a dosing pump and you have a major event you could always turn up the flow so you get 100% water change in 6-8 hours or so. I like that about the set up.

[dubbly]

So, I have had two setup that I have use successfully. At the core of both is a peristaltic pump. The design that you chose really depends on the size of your tank. I have used this config on a 14 and 29g tank.

 

Configuration 1:

Equipment:

2-Channel Peristaltic Pump

1 2.5 gallon water jug that starts empty

1 2.5 gallon water jug that starts full of new saltwater

 

I use a 2 channel dosing pump to pull out and put in water continuously from two 2.5 gallon jugs. One with new saltwater and the second with old. The pump moves about 75ml or 0.5 gallons every day or 3.5 gallons per week. This works really well for a 14g and pretty good for 29g tank. The pump that I have has an adjustable speed so you can make it slower if you want. I got the pump for somwhere between 75-85 dollars on ebay.

 

Quick check and I just found the same one that i have in the link below.

 

Pictures of this setup are shown.

 

http://cgi.ebay.com/Litermeter-Beater-2-Ch...=item3cb6b41676

 

Configuration 2:

If you want to conduct a faster change then what you do is you have the same pump or similar setup in a single channel configuration. IT will then pull out between 150 and 850 ml / hour (.2 gallons). Other pumps would do more. In this case I have used an ATO, powerhead, and float valve to refill the tank as water is pulled out. However, in this case, you need to account for evaporation by reducing the salinity level of your added saltwater mixture to account evaporation. I have done this without a problem as well.

 

Possible configuration: I suspect that a similar solution could be derived using an aqualifter but haven’t tried it. I like the accuracy of the peristaltic pumps.

[cchardwick]

That's a really sweet setup but it's a bummer that your max flow rate is only 0.5 gallons per day. It would be nice to be up in the 5 gallon per day range max for emergencies.

 

Here's my idea, it's a drip system that works by gravity. You control the drip into the tank with a valve and then you have an external overflow box that has a syphon tube, similar to this acclimation tank from Drs Foster Smith:

 

Reef Gently AccliMate Pro

 

As the drip system fills the main tank the water level in the sump increases, which increases the level in the external overflow which has a hole drilled in the box at a certain level and water overflows into the waste container.

 

 

Or this setup which requires drilling in the back of your nanocube.

 

 

Another option would be to pressurize the new water reservoir and put it underneat the tank and control the flow with a valve to get a slow drip.

 

[lakshwadeep]

Yes, it's inaccurate to say continuous water changes are too ineffective (on the other hand, 100% changes with proper adjustments of pH, temp, s.g., etc. can be done with little problems). Remember, in many natural reefs, the water currents create "water changes" for a specific space are both continuous and 100%.

 

You might also look into the equipment of chemostats, which are microbial growth systems that create constant growth by continually adding and removing equal amounts of culture media.

[dubbly]

You can do up to 5 gallons a day with my setup. Just need to use different tubing for the pump.

[wombat]

The peristaltic pumps aren't made to run this way, that's why it's so uncommon. Many people have looked into it, even called the CSR of the companies to all hear that the pumps aren't made for continuous use because it will burn out the motor faster.

 

Peristaltic pumps are designed as intermittent duty or continuous duty. I have plenty of continuous duty pumps that run non-stop 24/7 for many years. It's just a motor, and we all have plenty of motors running non-stop on our systems 24/7...

[wombat]

Hmmm. That's not what he said in reefkeeping magazine. Or it wasn't him I'm thinking of. But it doesn't even make sense that 30% matches 26%. Think about it

 

It does.

 

In order to determine the effectiveness of a continuous water change, use the following formula:

 

e ^ -(percent water changed)

 

So in this case the percent water changed would be 30%.

 

e ^ (-0.3) = 0.74

 

So 0.74 percent of the original water remains in the system, thus a 26% water change.

 

This calculation is from Randy's article.

[mikellini]

There is a difference between theory and practice. For instance, the amount of water changed may be that high, but nitrate reduction won't be since there are also nitrates being continuously added to the water. Ditto for other nutrients and biological waste. Also, evaporation plays a role in concentrating this over time unless you account for it by reducing salinity of incoming water, which in turn reduces incoming calcium and trace elements. As well, depending on where the in/out hoses are, efficiency can be further reduced.

 

Continuous water changes in a reef aquarium are nothing like the ocean

[cchardwick]

OOOO I like formulas LOLOL.

 

I saw a peristaltic pump brand new from Hong Kong on e-bay that said the life of the pump was 150 hours.

 

Hong Kong Peristaltic Pump, brand new

[mikellini]

The only peristaltic pumps I've ever used are IV infusion pumps. They're rated for something like 100,000 hours of continuous operation... At least that's what the company rep said at the seminar

 

Sort of necessary though. Don't buy anything from hong kong lol

[wombat]

There is a difference between theory and practice.

 

Well, in practice you can make the continuous water change MORE efficient than the theory. The theory assumes a perfectly mixed, homogenous solution. In practice you can add the water one place and remove it in another, such that you are removing dirtier water, say the water that enters your sump via the tank drain for instance.

 

Here is how the two compare, in theory. Green line is a good old fashioned water change, red line is a continuous water change. X axis is the percentage of new water vs. total system volume, y axis is actual water change effected. Notice that between 10-30% the two compare pretty closely. It is only at larger percentages where you start wasting a lot of water.

 

For instance, the amount of water changed may be that high, but nitrate reduction won't be since there are also nitrates being continuously added to the water. Ditto for other nutrients and biological waste. Also, evaporation plays a role in concentrating this over time unless you account for it by reducing salinity of incoming water, which in turn reduces incoming calcium and trace elements. As well, depending on where the in/out hoses are, efficiency can be further reduced.

 

What does any of that have to do with the price of tea in China? Those things are occurring regardless of how you accomplish a water change.

[mikellini]

Um no, and no. When you change out 20% of the water at once, you remove 20% of the nitrates. They don't go up while you're changing the water. And if you're changing at full salinity, you're also adding a sufficient concentration of calcium etc. Also, I don't get that table. Maybe I'm reading it wrong, but I've never done a 200% water change

 

Also, there really isn't such a thing as "dirty" water in a system with sufficient flow. The water in the sump is the same as the water in the display; same temp, salinity, and dissolved organics. The water in a reef tank is a "perfectly mixed, homogenous solution", for all intents and purposes. The only thing that you could argue that varies depending on location is dissolved gases

[cchardwick]

Yea, that table is confusing, but I think I can follow it. The green line should go to 100% max and end there, it's extrapolated out past 100% which doesn't make sense. And I think the green line is only one water change, so for instance if you changed 100% of the water on the X axis you get 100% actually changed on the Y axis. For the drip system if you change 100% of the water (X axis) you really only get 60% changed out (Y axis).

 

Also it does seem right that it would change as you get further from zero. For instance, if you do a 10% water change with the drip you are actually changing close to 10% because most of that 10% is old water, but as you move up the scale you are changing more and more of the new along with the old.

 

But there's also a paradox in this graph, because the new water becomes 'old' over time. For instance if it takes a whole week to do a 100% change, you may want to change out some of the week old water with the really old water. So to explain this paradox a little better, take a look at the graph, if you change out 60% of the water on a drip system you are really only changing out just over 40%. If you keep going to 120% on the drip system (red line, 120 on bottom axis) you are only at about 60% (left axis), but if you actually start over at the beginning after a 60% drip water change, considering all the water in the tank as old, you are now changing 80% (40+40). And if you only went up to 10% where they are almost equal and kept starting over at the beginning of the graph the drip would almost equal a 'regular' water change.

 

Confused? HE HE

[wombat]

Um no, and no. When you change out 20% of the water at once, you remove 20% of the nitrates. They don't go up while you're changing the water.

 

And? So they go up when you're done with the water change. What's your point?

 

The initial point that I responded to is that a continuous water change of 30% of the system volume is exactly equal (in theory, and potentially better in practice) to a 26% single batch water change. That is true regardless of the fluctuating nitrate concentration in the tank, or of any other fluctuating parameter.

 

And if you're changing at full salinity, you're also adding a sufficient concentration of calcium etc. Also, I don't get that table. Maybe I'm reading it wrong, but I've never done a 200% water change

 

The point is to show that you can change 200% of the volume (or 300% or 400%) continuously, but it still will not result in a 100% actual water change.

 

Also, there really isn't such a thing as "dirty" water in a system with sufficient flow. The water in the sump is the same as the water in the display; same temp, salinity, and dissolved organics. The water in a reef tank is a "perfectly mixed, homogenous solution", for all intents and purposes. The only thing that you could argue that varies depending on location is dissolved gases

 

Of course there is a difference, although it is minute. You can verify this yourself with sensitive equipment. If there is no difference between the water entering your sump and the water leaving it, the filtration/heating/etc must not be doing much at all and maybe you should consider removing it! How exactly can you make the assertion that the water in these two places is identical in dissolved organics? How are you measuring it?

[wombat]

The green line should go to 100% max and end there, it's extrapolated out past 100% which doesn't make sense.

 

The limits of online graphing calculators.

 

I initially just went to 100% for both, but it occurred to me that people doing continuous water changes may be doing even more than their total system volume.

 

But there's also a paradox in this graph, because the new water becomes 'old' over time. For instance if it takes a whole week to do a 100% change, you may want to change out some of the week old water with the really old water. So to explain this paradox a little better, take a look at the graph, if you change out 60% of the water on a drip system you are really only changing out just over 40%. If you keep going to 120% on the drip system (red line, 120 on bottom axis) you are only at about 60% (left axis), but if you actually start over at the beginning after a 60% drip water change, considering all the water in the tank as old, you are now changing 80% (40+40). And if you only went up to 10% where they are almost equal and kept starting over at the beginning of the graph the drip would almost equal a 'regular' water change.

 

Confused? HE HE

 

I don't see any paradox at all. It's just an equation describing infinitely small water changes occurring repeatedly. Nothing too mysterious about it. If you want to make a water change of y% every week/month/year, and you want to do it continuously, find the point on the red line that matches your desired y value and drop down to see the required x value. This is the percentage of your system volume you would need to continuously change.

 

This is the same curve at a more relevant portion:

[mikellini]

Don't play dumb. I know you're smarter than you're trying to make us believe. I'll try one more time, from a different angle.

 

The variable that you aren't considering is time. "Continuously" changing 20% of the water over the period of an hour might be theoretically close to doing a regular style water change, but continuously changing 20% over a period of a week is less efficient. By far. Time makes a big difference, because the old water gets older, as the OP said.

[wombat]

Time is not a variable in the equation for a reason. It doesn't matter how long it takes for the water change to happen.

 

Let's say you do the following:

1) Single batch water changes every Sunday by changing 26% of the water volume all at once.

2) Continuous water changes every week by adding (and simultaneously draining) 30% of the system volume over the course of the week.

 

In a theoretical world, perfect mixing, identical systems, yadda yadda, there will be NO difference in these two methods on their impact on dilution or supplementation of any parameter.

 

Immediately after you do the batch water change, the two should be identical. By Saturday, things will be quite different between the two systems. By the next Sunday, however, they will be exactly equivalent again. If you did this for several years you would see a sawtooth pattern for 1), and a smoother curve for 2). That is the only difference, aside from some wasted water with the latter method.

[cchardwick]

Wow, that makes my head spin thinking about it LOL.

[sean151]

My understanding is for it to be a continuous waterchange both have to happen at the same time. If this is true and not the usual "drain, then refill method" then you would be in fact draining your water you just added if it did take long enough to add your amount.

[cchardwick]

Well you wouldn't really be draining the water you just added, look at the graph and for the first 10% you drain almost no water that you added. It's only once you reach a certain point on the graph where basically you are counting all of the water ever added from the beginning of the drip water change, the further out you get on the graph the more the whole thing gets skewed. I think there has to be a different formula and a different graph. Say for instance you ran the drip for only 10% one day a week, and you start the graph over every time you start the drip water change. Then it's nearly equivalent to regular water changes, and you throw out the whole graph.