'Drip' Water Changes?

[wombat]

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.

 

Yup. For what it's worth, doing a drip with 10% of the system volume would be equivalent to a 9.5% change the old fashioned way.

 

To see how much of a change this results in over multiple runs, first find the fraction of the "leftover" water. In this case it'd be 1.00-0.095, or 0.905. Say you do this 4 times in a month. So 0.905 x 0.905 x 0.905 x 0.905, or 0.905^4, which equals 0.67. So 67% of the initial water remains. In other words, you did a 33% water change. Make sense?

[wombat]

You can also see how smaller more frequent changes effect the overall water change in a system.

 

Say you change 30% of the water every 30 days. That's a 30% change (duh).

 

Say you change 10% 3 times in 30 days. That's 0.90^3, or 0.729. That's a 27.1% change.

 

5%, 6 times in 30 days. 0.95^6, or 0.735. 26.5% change.

2.5%, 12 times in 30 days. 0.975^12, or 0.738. 26.2% change.

1%, 30 times in 30 days. 0.99^30, or 0.7397. 26.03% change.

0.1% change, 300 times in 30 days. 0.999^300, or 0.7407. 25.93% change.

 

So on and so on. You can see that as the changes become smaller and more frequent, you narrow in on a value. If you were to do infinitely small changes with infinite frequency, you would find that value is given by the exact equation I posted earlier. All hail the constant e.

[mikellini]

Your math is correct; you are wrong. We've stated our arguments, you're just not listening to mine. Have a nice day!

[wombat]

Considering you think Randy Holmes-Farley is wrong about basic math and chemistry too, I'll consider myself in good company.

 

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

 

Thought about it again, still makes perfect sense.

[wombat]

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.

 

 

You don't need to pressurize the new water reservoir in this case. The peristaltic pump will lift it. Keeping the reservoir below the tank is actually a preferable scenario; if you keep it above the tank it could potentially siphon in through the peristaltic pump tubing. Remote possibility, but it can happen.

 

I would also drill your sump if you're going to do this, and in a best case scenario the waste water would go to a floor drain.

[cchardwick]

Actually I was talking about pressurizing the container to eliminate the need for any kind of pump. If you had sufficient head space in the pressurized container it would keep the dripping fairly constant, but not as constant as a pump.

[d9hp]

Your math is correct; you are wrong. We've stated our arguments, you're just not listening to mine. Have a nice day!

 

What?

 

You don't have an argument.

 

 

Considering you think Randy Holmes-Farley is wrong about basic math and chemistry too, I'll consider myself in good company.

 

 

 

Thought about it again, still makes perfect sense.

 

Haha makes sense because you're right.

 

I don't really understand what the misunderstanding is all about.

 

Yes you waste some water doing back to back partial changes with 5g instead of doing 5g all at once...I do this with my system now because I've lost two shrimp on two separate occasions with what I had tested as identical water for the change (temp, pH, salinity, and alk)

 

So now I don't test anything except temperature and salinity. I mix a 5g bucket and use a .8g water pitcher to change. I don't turn any of my pumps off or anything.

 

I add a pitcher of fresh water and drain the tank until my float switch drops down again. This triggers the ATO to add RO/DI...but I only add a few ounces at a time and it only can do it once every twenty minutes max.

 

I then wait 4-5 minutes between pitchers until the 5g is empty and my dirty 5g bucket is full.

 

Is this as effective as a single 5g change? No. It's MORE effective for me. Salt is only $25 every other month for me...that's a fraction of the cost of maintaining this system and RO/DI water is essentially free since I drink it as well and don't mind paying for maintenance of the unit.

 

The drip change is ideal. I think it would minimize stress on the inhabitants and still accomplish the same task as wombat has demonstrate in detail.

 

If this system could be implemented so you could effectively change >50% every other day I think you'd see some real serious growth...as long as you're using a quality salt.

 

I use D-D H2Ocean and love the stuff...I would do my change with 15g a day if I could...the fish and inverts have never shown any reaction to the water change, where as at the old one required me to lower the water level in the tank etc. I used to do 2.5g changes the regular way and doubling the amount with the new way results in a larger change with less stress.

[lakshwadeep]

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

 

The nitrate reduction would be what was calculated because the calculation is based only on the number of initial impurities found in the tank and assumes the concentration is unchanged if there were no water changes done. You can see in Randy Holmes-Farley's article that small % daily changes, even when taking into account the production of nitrates, can be effective in reducing the total nitrate concentration (see figures (figures 8-13):

Finally, we can model the drop in nitrate when it starts high (100 ppm) and accumulates at a rate of 0.1 ppm per day, using both daily and continuous water changes. Figure 12 shows the data for daily changes. Again, continuous water changes exactly overlay these results (not shown). Figure 13 compares daily and monthly water changes of the same total volume. Clearly, the size of the water change is not particularly important, and both daily and monthly water changes of the same total volume have a substantial effect on nitrate. Larger total volumes changed obviously have a bigger effect on residual nitrate after a year.

http://reefkeeping.com/issues/2005-10/rhf/index.php

 

Evaporation can be compensated. "The only trick is to balance the input and output fairly well so salinity doesn't increase or decrease over time." -RHF

http://www.reefcentral.org/forums/showthread.php?t=938426

[mikellini]

I stand corrected. I figured that continuous changes would do little to actually reduce nitrates and would just keep them at a constant level, at least in practice. I guess not. But what about compensating for evaporation; you're still putting less calcium, magnesium etc back into the system for the same volume of water changed, correct?

 

I think this thread needs a poll. How many people are actually going to implement drip water changes?

 

Edit: I think I threw out the rest of your argument when you tried to say that the water in your sump is dirtier than the water in your tank. My bad

[cchardwick]

'DeeNineAychPee' hit it on the head when he said, "larger change with less stress". Bottom line is I don't really care how effective it is, even it it were only 50% effective, I can do massive water changes with no stress to my tank at all.

 

I can't figure out how to add a poll, but I know for sure I'll be doing drip water changes on my six gallon nanocube soon!

 

[lakshwadeep]

I think if you kept the input/output rates equal, the water level would be unchanged except by evaporation, which would allow the use of an ATO with a float switch.

[cchardwick]

Actually you wouldn't even need that. You could just adjust the output hose level and if it gets too low it would suck a little air, and peristaltic pumps should be able to handle air just fine. You would end up with a salinity in your tank slightly higher than the salinity in your new saltwater reservoir but it would reach an equilibrium and stabilize.

 

This is a really beautiful setup: No need for auto top off, no skimmer needed, don't have to worry about temperature or oxygen levels in the new saltwater, don't have to worry about evaporation or even water changes except once every two weeks to fill your reservoir, and you would never worry about shock to the system from the last water change or fresh water top off. And in an established tank you would never have to worry about depletion of trace elements, buffer capacity, swings in pH, etc.. In essence it would be an 'open' system, just like the ocean.

[wombat]

Actually you wouldn't even need that. You could just adjust the output hose level and if it gets too low it would suck a little air, and peristaltic pumps should be able to handle air just fine. You would end up with a salinity in your tank slightly higher than the salinity in your new saltwater reservoir but it would reach an equilibrium and stabilize.

 

This is a really beautiful setup: No need for auto top off, no skimmer needed, don't have to worry about temperature or oxygen levels in the new saltwater, don't have to worry about evaporation or even water changes except once every two weeks to fill your reservoir, and you would never worry about shock to the system from the last water change or fresh water top off. And in an established tank you would never have to worry about depletion of trace elements, buffer capacity, swings in pH, etc.. In essence it would be an 'open' system, just like the ocean.

 

Have you considered how much saltwater it will take to do 50% changes every day? Based on some back of the hand math you're looking at 120 gallons a month for a 6 gallon tank...seems like an awful lot of trouble to me.

[d9hp]

Personally I think tuning it to change a single 5g pail each week would be pretty impressive. That's still a ridiculous turnover rate and you're going to easily be able to keep up with heavy feedings. If I could change that sort of percentage each week on my tank I'd be dosing phyto and oyster feast every few hours!

[lakshwadeep]

While researching, I found this neat "automatic water change" system:

http://www.genesisreefsystems.com/categories.php?cat=7

[cchardwick]

That's brilliant, but $500 for a water changer? That's crazy.

[cptbjorn]

I've been doing continuous water changes for over a year now, I just use my ATO reservoir. They work great as long as you don't try to explain the math to someone >_>

 

the amount you need to change in this manner to be the equivalent of a regular drain and refill WC calculates out to be e^x-1, so for a 20% change you need e^.2-1=22.1%.

 

basically for small percentages the difference is inconsequential, and if you are in a situation where you need to change >50% you are probably screwed anyways lol

[cchardwick]

How do you use your ATO reservoir?

[cptbjorn]

How do you use your ATO reservoir?

 

when the ATO runs out of fresh water (about once a week) I fill it back up with salt water and then run a drip line out of the tank into a bucket. I run the drip until the ATO is empty again, fill it back up with fresh water and I'm good to go for another week.

 

Takes almost no work and nothing in the tank even notices a 35% WC.

 

edit: also while I'm doing it it feels kinda like the water jug riddle from die hard 3 which is a big plus

[cchardwick]

Wow, that's brilliant! You just have to remember to stop draining before your ATO runs out LOL. Which ATO do you use? I bet its cheaper than a peristaltic pump.

[d9hp]

when the ATO runs out of fresh water (about once a week) I fill it back up with salt water and then run a drip line out of the tank into a bucket. I run the drip until the ATO is empty again, fill it back up with fresh water and I'm good to go for another week.

 

Takes almost no work and nothing in the tank even notices a 35% WC.

 

edit: also while I'm doing it it feels kinda like the water jug riddle from die hard 3 which is a big plus

 

####.

 

That's crafty!!!!

 

Definitely going to think about how I can implement this.

[pweissma]

The graphs and formula of A=e^(-P) where P is the percent of water used for the water change and A is the percent of water actually changed assume simultaneous removal of old water and addition of new water, also, this water change is done in an instant or in a time too short to be relevant.

 

The formula can be derived by solving the differential equation dA/dP = -A which says that the decrease in the percentage of old water as new water is added is equal to the percentage of old water left in the tank. Again this applies to an instant in time.

 

If you consider "continuous" to mean occurring throughout time then this isn't really a continuous water change. Perhaps the term "simultaneous" is better.

 

A "continuous" water change would include the simultaneous addition and removal of water but also be continuous through time. Math here is but quite different since time needs to be considered.

[pweissma]

I think if you kept the input/output rates equal, the water level would be unchanged except by evaporation, which would allow the use of an ATO with a float switch.

Yes, for continuous water changes you should keep input and output rates equal and then a typical ATO can be used to counter evaporation. To do this Stenner makes nice peristaltic pumps that put two heads on the same motor.

[cptbjorn]

Wow, that's brilliant! You just have to remember to stop draining before your ATO runs out LOL. Which ATO do you use? I bet its cheaper than a peristaltic pump.

 

the ATO is one I made that uses an aqualifter, it works well for small tanks but if the WC is over 5 gallons I'd do something bigger since the aqualifters aren't really made to pump large volumes of water like that.

 

the plus side to the aqualifter is that they become extremely noisy when they run out of water and start to pump air, you'd have to leave the house to not notice the sound.

[wombat]

Just to clarify something, there is no way you can trust two peristaltic pumps to "match" flow rates. Sorry, it just ain't going to happen. Slight differences in friction loss, motor speed, etc. will always make a difference that will add up to a flood over time. Also, picture what will happen if one of your pumps fails.

 

The safest way to do this is to have either your addition or drainage (but NOT both) regulated by a peristaltic pump, and the other by gravity.

 

Gravity never fails, pumps do. You also need to keep in mind what will happen if power shuts off completely during an outage, and size your sump accordingly.