Water Changes- Why, How Much, and How Often

[RTR]

Water Changes- Why, How Much, and How Often


Once upon a time, not really so long ago, there lived a lovely theory of the “Balanced Aquarium”. You had this glass box, with stainless steel edges, a slate bottom, a stainless steel hood with a couple of incandescent light bulbs. If you were going first class, the light bulbs were tubular “showcase” bulbs. If you were traveling economy, the frame was painted metal, not stainless, and so was the hood. The assembly sat on a wrought iron frame. In this tank you had some sand, some plants, and a pretty good selection of fish. The first-class tanks included a box filter loaded with “angel hair” (spun glass). Or for the truly advanced hobbyist, an internal hang-on box filter was used with layered gravel or sand, charcoal, and spun glass. The air pump that provided water movement for this included a metal flywheel, one or two cylindrical pistons, and astoundingly noisy valves. It made slightly more noise than a heart-lung machine and had a tendency to walk across the bottom of the aquarium stand and fall off with a crash. These pumps weighed about the same as full canister filter. The crash only occurred between two and four AM. The crash would also disconnect the airline tubing, so when you came in to correct the situation, you were brought fully awake by the puddle into which you stepped. Your valuable water was lost in the carpet. Change water? Why? It was conditioned, aged, mature water. My original LFS actually sold the stuff- clear amber in color; you really needed to get some to start your tank.

The esteemed William T. Innes was one of the radical aquarium keepers, he actually suggested changing part of the water on a regular basis- 10% per week in winter, 25% per week in summer. Shocking. There was lots of controversy on this when I was young. There were numerous very fancy hand-blown glass devices that served as dip tubes for extracting debris from the bottom of the tank. It was suggest to me that I dump this into a pitcher, allow the gunk to settle, and pour as much water as possible back into the tank. That way you only had to add the minimum amount of “raw” water.

Well, eventually Dr. Innes’ position won out, but I understand that there are still holdouts around who do not advocate water changes beyond some absolute minimum well below Dr. Innes’ suggested levels. I’m sorry, but to me this like telling people not to vacuum conventional undergravel filters. Where do they think the fish poop, uneaten food, plant debris, et cetera, is going to go? We do add food to our tanks- though in the mythical Balanced Aquarium that was frowned upon also. We also add water to compensate for evaporation. Minerals and solid wastes do not evaporate.

Water is wonderful stuff, the universal solvent, responsible for life on earth as we orbit the sun in the wonderful region where water is liquid- over much of the planet- though that is hard to believe looking out my window right now. Fish live in it. They eat in it. They poop in it. Skipping over the actions of nitrification and heterotrophic bacteria, all the food we add to the tank ends as gunk on the bottom of the tank, or incorporated into bacterial or algal films on various surfaces (or even suspended in the water column), or dissolved in the water. Lots of things are dissolved or suspended in the water. In a mature tank, we measure one: the nitrate concentration. We do not measure the dissolved organic compounds (DOC), the suspended bacteria or algae. Sometime we will re-visit DOC for a good horror story. It includes anti-metabolites, toxins, colorants, and many unseen undesirables.

Nitrate concentrations are not just used for themselves. Nitrates are much less toxic short term than their precursors in nitrification, ammonia and nitrites, close to two orders of magnitude less toxic. Long term is somewhat less comforting. Perhaps one order of magnitude (10-fold rather than 100-fold) if you are generous. Part of this borders on the "survive" versus "thrive" arguments. Can we say that I am of the “attempt to have your fish thrive” group? When I advocate a particular water change policy, I use nitrates as the measure. The water change however does not know that. The siphon removes all the DOC and other undesirables in the same volume of water without discriminating. My hope is the same relative change in these unmeasured nasties will be as beneficial as the measurable change in the nitrate concentration. Does that make sense? Nitrate alone is far from the whole issue in water changes, it is just an accessible handle we can grab and measure.

Okay, that has to be longest introduction to a simple technique ever given. How much water do we change, how often do we do that, and how can we tell we have done it right? We have this imaginary tank in our living room. It is a nominal 29-gallon tank. My 29 measures 30 1/8” side-to side, 12 1/2” front-to-back, and 18 5/8” tall. By those outside dimensions, it would calculate to 30.36 gallons (*). Ha! The glass is not anywhere near that. And the glass has thickness too. The inside of the tank is something like 29 3/8 x 11 7/8 x maybe 17 1/2” effective depth to a practical water level. That is 26.4 gallons. Then I have a thick substrate, which displaces a significant amount of water. The actual fill volume of the tank is about 22 gallons. But, I cheat. The tank manufacturers assign these imaginary numbers to the gallonage of our tanks. I use those numbers for water changes. If I post that I do a 15% change on that tank every week, I change 29 x 0.15 = 4.35 gallons, 4 1/3 gallons, or somewhere between 4 and 4 1/2 gallons. Granted that I am slightly neurotic about a few little things, I have 10-15-20-25% of nominal volume marked on the sides of most of my tanks. I vacuum the substrate by Python down approximately to my target mark, then refill the tank. It this particular tank, that 4 1/3 gallons is almost 20% of the actual volume. It is 15% of the nominal volume. If the maker can lie to me, I can lie to myself. I will admit that when I post such information I try to say 15-20%, so I am covered whichever way you measure.

How often do I do this change? If you ask I will calmly answer every week. If you pin me to the wall on the topic, I will confess that it is really more like every week to 10 days. Even the anal need some breaks. Sometimes I hold the schedule well, and am much happier with the world. Should a tank get only three changes this month, the world will not end, the fish will not die, and I will be only slightly guilty. I favor frequent changes because they do the best job of maintaining steady water parameters. The pH, hardness, nitrates, DOC, clarity, will not have shifted that much since the last change. If you wait two weeks, those things will have changed twice as much. Somewhere along the line you are increasing the stress on the fish and the system itself. The more frequently the water is refreshed, the lower the stresses of the system and its inhabitants. Most fish “like” water changes; they seem energized by them, so long as they do not involve so great a change in water parameters that they are inducing stress and even shock.

How can we tell that we have done it right? Easy. We test for nitrates. You pick a level of nitrates that is comfortable for you. Many people select 20-30 ppm. I aim for lower concentrations, 5-10 ppm. I do that in part because I have a lot of plants and am not a big fan of algae, I have enough of it now, thank you very much. While you are getting your feet wet (bad joke) with monitored water changes, keep some sort of record of your nitrate readings. If you start out at a level too high for comfort and it is going down gradually, you are winning. If it is rising, you need to re-evaluate. More volume or more often, your choice, so long as do not shock the fish with too great a water parameter change. Are you overfeeding? Overcrowded? If you are maintaining or decreasing very slightly, you did not need to read this article.

Water changes are one of the easiest things you can do for your tanks and fish, and will do more to support their health and longevity than the most high-tech filtration and control systems can do without water changes. It is a very good habit to develop. Don’t really siphon into your shoes (yes, I have), but do get your feet wet.


* To calculate the actual volume of a rectangular tank, measure (in inches) the inside length, width, and depth (to a realistic water level, not to the rim). Multiply these three numbers together to get the volume in cubic inches. Divide that product by 231 (cubic inches per gallon) to get the actual volume without gravel, rocks, etc. If you want the working volume, you must measure the first time you fill the tank (the only time I ever carry buckets).

[Sylvia]

Thanks for the article! I know I feel guilty if I miss a water change . It is nice to see how fish are happier afterword.

[fishmama]

hi1 I LOVED YOUR WATER CHANGES EDUCATION!

i have a question....i have a corner tank. it's a triangle.
the manufacturer says its 36 gallons.

it measure as follows...

37 inches for the bowed fron
18 for the height
and 22 inches for each of the other two sides of the triangle.

how do figure it?
thanks!

[joephys]

I posted in your other post about it, but I'll post it here

Its basically a quarter of a cylinder. The area of the base is the quarter of the area of a circle divided by four.

A=pi*r^2 Where pi is (3.14) and r is the radius, or the length of the straight side.

Then for the volume multiply by the hight. Now you have the volume in cubic inches. To convert to gallons, divide by 231. Since its a quarter of a cylinder, you need to divide by 4, then you have the volume of your aquarium

so for your numbers

A=3.14*22in*22in=1520in^2

V=1520in^2*18in/231/4=29.6 gallons

I think you had slightly different numbers posted on your other post, so the volume is close, but a little different.

[OrionGirl]

What are you trying to measure? The volume per vertical inch? Easiest method is going to be to remove a known volume (ie, 5 gallons) and then measure. Bow tanks are a bit trickier to calculate, but you can use the basic formula for a rectangle and then divide in half (ie, .5(w X l X h) to get a ballpark figure. But measuring it as you remove is going to be the best way, since you don't have to account for displacement of water by objects (filter, rock, wood, plants, etc.

[RTR]

I do pretty much as already suggested - I measure by added and removed volumes.

I hate buckets of water. I have carried too many buckets of water in my life. I am as married to the Python as to my wife. But when it comes to new setups, I measure as I fill so I get the actual working volume, but not exactly the world tightest data. These are fish tanks, not brain surgery. Once i know the working volume, I figure out how much I want out per partial and mark the corner of the tank. Python to that mark and I am happy, the fish are happy, and I don't have to tote any more buckets until I do another setup. To date, nobody has ever asked what those funny marks are on my tanks.

[Trixie]

So, uh... RTR.. umm... What are those marks on your tank?

[OrionGirl]

We did much the same thing for the SW setups. A wax pencil, on the back corner where it's visible but not obvious works well, and can be adjusted easily at need.

[wesleydnunder]

Originally Posted by Trixie

So, uh... RTR.. umm... What are those marks on your tank?

---- disturber!

heh

Mark

[RTR]

Sometimes I do cheat - some of my tanks use stick-on thermometers to judge partials. Drain this tank down to 78 F and refill for a 50% partial. But I rarely talk about that technique as folks think I am adjusting the temp rather than changing the water. Measure do not have to be rational, they have to be functional, right?

[Trixie]

LOL! Absolutely. What is most important is that the water gets changed regularly. And that's what we do.

[zippo]

I liken wc's to flushing the toilet, you can either give it a full flush or a partial one, but for gods sake flush it! Your fish will love you too.