View Full Version : Water changes
I hear conflicting opinions about water changes, the frequency, the amount, you name it.
I have a fully cycled (has been for a while) 20 gal. with an AquaClear 150 filter. It is fully stocked and doing very well. At this point I've been doing monthly water changes (25%), without trouble, but I read a lot from here that I should be doing them once a week, every two weeks, once a month, and taking more water out. Could someone please clarify this? Thank you. I'd hate to think I'm stressing my fish out without realizing it!
OrionGirl
05-07-2004, 1:17 PM
Planted or no?
If it's not planted, test for nitrates. The goal is to keep nitrates below about 20 (yes, there are different number given for this, 20 is a decent midway, IMO). So, if your nitrates are 60, you may want to increase water changes. If your nitrates are under 20, you're probably doing enough now, and can stick with the same schedule.
One other consideration is evaporation. If you have lots of evaporation, rather than adding lots of top off, you'll be better off doing more water changes. Evaporation results in concentrating the wastes, while water changes remove them.
If this is a planted tank, nitrates are useless in determining the need for water changes. You'll need to establish a schedule and then stick with it regarding water changes and ferts.
Ok, OrionGirl, and thank you. The tank is not planted, so my first job is to pick up a kit for testing nitrates (yeah, I'll admit it, I don't have one). Evaporation is quite minimal, and when I did notice a slightly lower level, I did do a water change, so I guess my instinct was right on that one. Off I go to get a testing kit. Thanks again!
OK, I did the test. It was up at the 110mg area! (I just did a water change a couple days ago, too). So I did about a 40% water change and re-did the test. It's still around the 110mg range. I tested the water out of the tap (after de-chlorinating it)and it registered 0, so that's not it. Now what?
The odd thing, too, is that the package (Hagen Nitrate test kit) said to do a 25% water change if the test shows above 110mg! That's a far cry from 20. Any suggestions?
aquariumfishguy
05-07-2004, 9:58 PM
Huh?! :confused:
When we say 20, we are talking parts per million... or 20 ppm.
MG is not the scale we are going by. Could you report the readings in PPM?
OK, I'm looking at the test booklet. It does tests for Nitrates from 0 - 110 mg/L (ppm). So I guess 110 mg/L = 110 ppm. I'm slightly confused myself, as 110 seems so high, yet the booklet says "if Nitrate concentration is above 110 mg/L, do a 25% water change." (Everywhere in the book refers to "mg/L", not "ppm". But it does sound like it means the same thing.) Anyway, OrionGirl , whose opinion I've learned to trust after reading on this site for the last several months, says to have the nitrates at 20 (ppm, I assume) or less. My booklet says 110. That's nuts. What's even worse is my nitrates are 110 ppm, and I just did a water change two days ago. I even tested plain tap water, de-chlorinated, and it was fine (at "0"), so that's not it. My tank is psycho!
Richer
05-08-2004, 2:14 AM
Like many things in this hobby, everything "depends." Personally, I think nitrate levels are fine if they are under 40ppm. However, each person is different. In terms of nitrates, my motto is, keep it as low as possible. My tanks all read nitrate levels under 10ppm... because I'm a light stocker, and a water changing nut :D.
Everytime someone asks me how much water to change, and how often, my response would be "at least once a week, 30-40%... more if you feel like it." If water changes are done often enough, the tank water will be quite simliar in terms of pH, hardness, etc. compared to your source of water (generally the tap). This is a good thing. If a disaster happened (ie. accidently dropping a tub of food into the tank) very large water changes can be done with little or no consequences. I can confidently say that I can do near total water changes on all my tanks, and all my fish will be perfectly fine. Actually... every month or two, I do two 50% water changes in a row on my tanks, on top of my weekly 50% water change. Yes, thats a lot of water changing, but believe me, my water levels are pretty good.
Before you run off doing more frequent water changes, you need to test the water in both your tank and your tap. Put some of your tap water in a shallow bowl and let it sit there for a night. After the water has been given a chance to outgas any dissolved CO2, test its pH and maybe KH. Then test your tank's pH and KH. If both levels are quite simliar, then go ahead and just start doing more frequent water changes. If both levels are different, start off slow. Something along the lines of 5-10% weekly and work it up to a good level over the course of a few months. Doing so should slowly match your tank's water parameters to your source water.
Anything to keep in mind, some people do their water changes according to nitrate levels (ie. if the nitrate levels exceed 40ppm, they do a water change). Others just have a regular routine and stick with that. I am one of those people with the regular routine (with the occassional very large water change stuck in there). Admittingly, I rarely do water testing on my tanks. I did do tests right after the tanks were stocked for a couple of months, but after I got my routine pinned down, I stuck to it. I only do tests every now and then... perhaps once every couple of months, just to see how my water changes are keeping up with my fish. I think it just makes it easier for me... I'm lazy, and I don't like working testing kits ;)
HTH
-Richer
aquariumfishguy
05-08-2004, 9:39 AM
Ok, I am sorry. After going and looking at my own test kits which I hardly ever use, I did see the (mg/L) sign and indeed, that equates to ppm. Sorry for the confusion. :D
Anyway, that said, 110 ppm is a deadly (toxic) level for fish. Actually, anything over 80 ppm is very bad for your fish if they are exposed longterm to that.
For now, you should focus on getting that level down to 40 ppm. Once you've shot for that level, you should try to reach 20 ppm. If you can do steady water changes on a regular basis then a nitrate level of 20 ppm shouldn't be hard to accomplish. Good luck...;)
Agree w/Richer's comments. Very strongly agree with his warning not to start with massive changes if your tank has drifted far from tap water or other source water parameters. If you measued TDS the diffrences would likely be even more striking than measuring nitrate alone. Large changes in water parameters in a short time can be an osmotic shock to fish. Bringing the differences down slowly will avoid that, allowing the fish to adapt to the better conditions. Then setting the routine changes on such a schedule as to keep the parameters from drifting again is good.
Periodic very-large scale changes are good also - if there are not large detectable differences in tank and source water (pH, GH, KH, nitrate). Those changes help balance out anything we can't/don't measure.
You guys are all great. Thank you for all the information. I'll be doing another water change in a couple hours, and then I will re-test the nitrates. Hopefully they are down at least a little! I will post the results, and then keep it up to get the levels down. After what I've heard about Cycle messing with nitrate levels, I've stopped using it, so that should hopefully help, too.
The nitrates are coming down!:) They're still high, and since the test kit goes from 50 ppm to 110 ppm, it's impossible to tell exactly where I'm at, but while it's above 50 still, it's below 110, which is a great improvement. And no Cycle was added! Anyway, I will keep up the regular water changes (I'm doing them every other day), and when the nitrates are down, I will do them weekly, at about 25%, except for the occasional big change, like suggested. Thanks so much for all the advice!
You cannot arbitrarily set a predicted required percentage change until you get there. In effect you have to see how much nitrate is generated in your tank weekly and do sufficient partials to remove all of that, plus a bit for margin of error and safety. Every tank is different, depending of bioload and feeding habits.
Make sense?
aquariumfishguy
05-09-2004, 1:20 PM
Makes total sense.. uh, to me anyway. :o
For example my 40 gallon tropical tank needs bi-weekly water changes but my 55 gallon goldfish tank needs weekly water changes, just to keep the nitrates under 20 ppm. ;)
Yes, I understand, too. Each tank is unique so each tank is treated differently, on a different schedule, depending on it's needs, etc. Thanks for clarifying that!
Just an update to say my nitrates are now down below 10ppm. Yipee! Thanks again to all of you for helping me.
aquariumfishguy
05-10-2004, 9:44 PM
hmmm... if thats true, I am very happy for you. :D
But that seems very quick that your nitrates would drop to below 10 ppm after being over 100 ppm. :confused: It seems like that alone would kill the fish.
Well, I thought so, too, but what do I know? I just re-did the test and for sure it's a pale pink. When I first started this, the color was a very dark fushia. The PH is 7.2. I did water changes of about 30% (I took out 6 gal from 20 gal tank) every second day. Maybe it was too harsh for the fish. Cause you know what? My pleco died today. For no apparent reason. Everyone elso seems fine........
Okay, ready for a math exercise? Calculator ready?
Start with 100 liters actual volume(for simplicity) at 100 ppm nitrate (or anthing else that linear scale, not log scale).
1st change at 10%/10 liters, replacement water 0 ppm, post change titer 90 ppm.
2nd change, 10% from tank now at 90 ppm, post change titer now 81 ppm
3rd change, 10% from tank now at 81ppm. post change titer now 73ppm.
Get the message? Serial changes at the same percentage volume remove less actual material each time. The titer reduction is the same percentage, but the starting liter is lower, so less total material is removed each time...i.e., diminishing returns.
If the 2nd change had been 12%, 12 liters, 90 ppm - (90ppm x 0.12 = ~79) = ~11 ppm removed, just a tad more than the first change.
Serial changes need to move up in volume slightly each time to speed the process and maintain the efficiency of removal per change.
Starting too large in percentage is a shock (this is Old Tank Syndrome, whether the tank is old or not). Staring small and increasing volume changed each time is less shocking with still good removal efficiency. Maintaining the same volume each time is less efficient each time (ignoring the small increases of nitrate titer each day or per two days. You are doing the same work, but getting "paid" less for it. When you start too large, your biggest "cost" is the first change (stress to the fish), much less each time after that. Starting a serial change sequence no greater than your usual change will minimize shock to the fish, and reducing the time between changes and increasing the volume a bit each time will maintain efficiency and not increase fish stress.
Does any of that make any sense to anyone?
Serial changes starting at large change percentage are risky in OTS.
Serial changes starting at small percentage change per time, not more than past customary change volume is best, but with increasing change volume/percentage each time will maintain effciency and have no addition stress on the fish.
HTH
OK. I think. Actually, while some of your explanation had me going back and re-reading other parts, and some of it had me cross-eyed, I understand enough to let me know basically what I did wrong. I wish I had known. I feel like crap for killing my pleco. Start smaller, and increase gradually to get better results ,and stress fish less.
Thank you very much for spelling this out for me. The time you took taught me a lot, and I learn from my mistakes!:(
sdb - don't feel too bad, we have all made our own share of tank blunders and did un-intended damage to fish. The point is that you have learned from it.
Water changes seem such a straight-forward thing, but it not always so simple. When something is off with the tank, massive change may well be the right thing if it is an acute toxicity (get the introduced toxic material out ASAP). But if it is something that built up slowly with time, massive change can be shocking to the fish, so you need to start small and increase later, allowing the fish time to adjust to better water conditions. It is counter-intuitive, but if fish have adjusted to bad water, good water is too different from what they are accustomed to living in - you have to give them time to re-adapt. Many folks get this a little mixed up and call it pH shock, but it is really an osmotic effect on the fish.