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DKRST 07-27-2011 05:28 PM

Tank maintenance & water change frequency
Is one, large, weekly change any better than two smaller? Is there any reason to cut back to one change/week or less?
Maintenance routine: Water change on Wed and Saturday, about 30% of water volume each change (estimate actual water in tank @ 45-50 gallons). Dose with Flourish comprehensive on M,W,F. Daily dosing with 5ml of Excel (I don't overdose Excel w/water changes).
Tank info:55 gallon, heavily planted (amazon swords, ozelot sword, brazilian sword, queen radicans, rosette swords (a bunch), rapidly growing rotalia, cabomba, myrophillium, anubias, frogbit, water sprite, and pennywort. Inhabitants: 4 angels, two bristlenose plecos, 5 pepper corys. Filter: Eheim 2215 Light: T5HO x2 (with fiberglass screening to cut light levels). Parameters: ammonia, nitrate, nitrite all at 0. pH @6.8
I guess with my overdosing of the flourish comp, I'm (expensively) simulating EI dosing to a degree. To date, everything's working well in the tank. I kind of like my weekly "tank time". Without repeating all over again, I was wondering what folks thought about my water change routine? Note: I am bad about overfeeding!

zof 07-27-2011 06:40 PM

I dread water changes, in fact so I usually only do it every two weeks now but then my tanks are heavily planted, lightly-moderately stocked and nitrates rarely get above 10ppm.

I can see a few issues with doing a water change greater then 50% though, one, established tanks pH typically differ from the pH coming from tap due to organic decay. Two the more water you change at one time the more likely you can temperature shock your fish if your not really close to the tank temp. Three I think its less stressful for the fish to have ample room while you change the water. Four the lower you take the water level the more likely you will brake steams off of the taller plants if floating plants get stuck on those plants.

kitten_penang 07-28-2011 09:00 AM

i dose my tank every monday and thursday so every sunday i do a 20 percent water change and it works well for me

Beaches 07-28-2011 09:44 AM

If your routine is working for you and your fish DKRST, then I wouldn't change it. What works for one person, may not work for another, finding out what does work for your tank/fish is the important thing and then I would stick to it.

I prefer to do smaller water can always do more if need be. I agree with zof's comments, plus any major fluctuations caused by large water changes may also affect/hinder the nitrifying bacteria.

AbbeysDad 07-28-2011 09:54 AM

DKRST, this is an interesting puzzler my friend!

If we look at fresh water in nature we would conclude that some areas receive almost daily rainfall (e.g. the rain forest) while other areas receive a little rain now and again and/or the torrential rain fall. We might also note that rainfall varies at different times of the year.

In the case of our tanks, with the purpose of diluting dissolved yuk, I'm not sure it matters as long as we do it often enough, in quantities sufficient to 'freshen' the water by diluting the existing water. We might say that a 25% biweekly change is nearly (but not exactly) the same as 50% weekly.

Now as to the amount, there is something to be said for the tank water condition as compared to the tap. If one adjusts for pH or has wood or other elements that alter pH, there may perhaps be an associated negative relative to the quantity of the water change. I have not seen any negative effects doing 30%-50% water changes (but I do not adjust for pH or have anything that acidifies the water).

So, bottom line, I think your method is fine, but probably not significantly different to doing a somewhat larger water change weekly. I have been doing a nearly (but not quite) 50% water change weekly and it seems to be working fine. :-)

kitten_penang 07-28-2011 09:56 AM

i like using ro when i do water change it does wonders to dilute the gunk lol

DKRST 07-28-2011 10:42 AM

One thing I should have mentioned. My tapwater comes out at 7.0, and it's soft. My tanks are all within just a couple of tenths of pH 7, so the potential pH "shock" it's not an issue. For me, I'm more worried about stress of pH change from water replacement as my tanks drift lower over time (due to tank wood) so that is one reason I prefer more frequent water changes. Temps not an issue, I make certain the temp matches before it goes in the tank (I'm an old fashion bucket-dumping kind of guy!).

Mikaila31 07-28-2011 11:11 AM

I do 50-60% weekly on most my tanks. I'm honestly not worried about pH changes or temp changes. I don't bother with matching the temps exactly. Sometimes I will do cold water changes if the tank is hot, enough to drop the tank temp 4 degrees or more. Any healthy fish should not have a problem with these changes.

DKRST 07-28-2011 12:37 PM


Originally Posted by Mikaila31 (Post 754908)
I do 50-60% weekly on most my tanks. I'm honestly not worried about pH changes or temp changes. I don't bother with matching the temps exactly. Sometimes I will do cold water changes if the tank is hot, enough to drop the tank temp 4 degrees or more. Any healthy fish should not have a problem with these changes.

Do you do a single change weekly? If I remember, you dose dry ferts?
I don't generally do a 4 degree temp difference, but I often estimate the water temp by the (error-prone) finger-dip comparison. I have verified the temps and I'm usually within 1.5 degrees +/- using just the finger-check method.

Byron 07-28-2011 12:38 PM

I'll add some math to the issue. With respect to just the volume of water changed, the more you change the more "crud" will be removed. Crud refers to dissolved (liquefied) fish waste, urine, pheromones, etc. Crud cannot be "removed" by filters [except to some extent live plants] so only a water change will remove this pollution--and pollution is exactly what it is. In natural waters it would be removed rapidly by water movement in streams, thermal currents in lakes, rainfall and evaporation, etc. A water change is essential to remove it from a closed system aquarium.

Crud is constantly being added to the water by the fish. The less water that is removed and the less often, the more crud builds up. So mathematically it is better to remove more water and more often.

The value of larger weekly water changes over smaller twice weekly changes is in the level of pollution that remains after each. The fish will be exposed to less pollution for part of the week if a larger water change is performed, as opposed to changing less water more often which leaves more pollution in the tank throughout the week.

The biology of the tank should determine the frequency and volume of water changes. The fewer fish and more plants and in a larger volume, the better the biology should be--theoretically at least. This is why some natural planted tank aquarists can advocate a water change once every six months, or less; but they are quick to point out that this works in tanks thick with plants and a modest fish stocking. The more fish in a given volume of water, the more essential are larger water changes and more often.

You can raise 30 discus fry in a 40g tank by doing 95% water changes several times each day. The fish will grow fast and be very healthy. The same fish in the same tank without the water changes will be poorly developed and stunted, if they even live through it. Clearly it is not the tank size here, but the water changes. And there is enough evidence that this is not a matter of nitrification alone, but the "crud" that we can't see and can't measure with test kits.

Allowing a drop in pH or a rise in nitrates to dictate water changes is very unsound. By that point it is too late; the damage to the fish has occurred. Health problems down the road, including a premature death, can be traced back directly to poor maintenance.

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