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I was just told this and , call me crazy, it makes sense to me. We have fairly hard water in my area, and alot of fish prefer softer water and many prefer more stable water conditions. Someone told me that doing small water changes once or twice a week can actually increase the hardness of the water in your tank over time. The water evaporates, but all of the minerals that make the water hard are left behind, so doing small water changes doesn't remove enough of this concentrated water to keep the hardness stable and although it make take a very long time, the hardness of your water will gradually increase.
Responses??

Hi,
IMO, it sounds like someone trying to rationalize their
lack of frequent, regular, water changes.
If you top off the tank during the week for evaporation,
and then weekly, remove 10% or 20% of the tank, the
minerals this person is concerned about will not be allowed
to build up.

If your water is harder than you prefer, for the fish
you are keeping, you can dilute it with distilled or
RO water.

But... Keep doing your normal, weekly, water changes of
10 - 20%. Rain fall, and flooding is natures way of
"changing" the water outside. Water changes are your way,
and because your tank is such a microcosm of nature, it
should be done weekly (depending upon the fish load).

Frank

-->>> The Confidence of Amateurs, is the Envy of Professionals <<<--

It makes perfect sense to me and it's been written in many places, but this is true for all dissolve solids in the water, not only GH. If, for instance, your water has X tds, and then water evaporates (only H2O), the ratio of tds per H2O rises, meaning higher tds (X+Y). Then when you top up your tank with your tap water which have the X tds, it does dillute the current tds, but it's still higher than the original tds. We can say that now your tds is X+Z (and Z&lt;Y). So yes, theoretically it is correct. That's why in marine aquariums they should first top up their water with unsalted water, but make water changes with the same salinty of the tank. That's why people who keep soft water fish (and go through the hassle of using r/o) top up with pure r/o water before changing the water. As I said, this is theoretically correct, but for the general community aquarium this does not make a big difference.

There is this subtle distinction here between top up water and water changes, and again, if you don't already use r/o water to try and keep your GH, KH or TDS down, it shouldn't really bother you.

Hi,
I think "we" are getting into the area of "splitting hairs"
and the realm of the inane here.
The origional question was one of performing small water
changes at a regular interval, weekly, or even twice a
week. (Unless one has a huge bioload in a given tank
twice weekly sounds kinda extreme.)
We all know that as water evaporates, only water leaves
the tank, concentrating the TDS.
Top offs normally are done with fresh tap water.
So yes, the certain elements could be said to be
increased above that of the Origional Water.
Then a 10 or 20% water change would dilute the tank water
back down to some value, perhaps slightly higer than
the origional, and each weekly water change would add
some slightly higher value to the "Origional Water" values.
I believe it would take a chemist and a laboratory to
determine the increase. Certainly it is so small that
our test kits could not resolve the change.

At that rate I wonder how many decades of water changes
it would take for the water to require a 50, or 75, or
100% water change to bring the water back to its Origional
Water values?

In this specific tank, I would do water changes with a
blend of tap and either distilled or RO water to maintain
a desired hardness. I would do the changes each week,
slowly dropping the water chemistries to the desired point.
Once that is done, you would need to determine the ratio
of Distilled or RO water to tap water so that one knew
that if 5 gallons was disposed of from the tank, the new
water should consist of xG of tap and yG of distilled or RO
water, mix throughly, and pour in.

Now that we are done splitting hairs, lets return to the
practical.... What are the values of the origional tank
in question and what does the owner want them to be?
Unless we are talking fish of the extremes, ie, discus
&amp; rifts, this could all be much ado about nothing.

Nearly every fish today, is farm bred and not wild caught.
The key to those fish is more a stable pH than a specific
general hardness. Most every tropical fish will thrive
in water that is 3-11GH (50ppm-200ppm).

Frank

-->>> The Confidence of Amateurs, is the Envy of Professionals <<<--

Frank, I agree that it shouldn't bother most people, and I said so. I also agree with everything else you've said and I also think that water changes are important for the fish, and this should not encourage anyone not to do water changes. I also agree with everything else you've said.

However, you know this forum better than I do, we sometimes like to get into the area of "splitting hairs" and I think this was exactly that kind of post, so I've split my hairs.

I thought this might stimulate some interesting discussion and hypothesizing. My pH is 7.5 and gH is 11-12 (180ppm) for a 25 gallon tank - I was doing very small water changes twice a week (between 1-3 gallons) because I wanted to get rams and another person had told me smaller, more frequent changes would keep the water more stable for the rams. I would like to lower the pH and hardness a little for the rams, but as someone has already pointed out, consistent parameters are more important than trying to get the parameters to optimal levels for the fish in the tank and risk having fluctuations that could be very stressful for the fish. How would it affect my ph and hardness if I began doing 5-6 gallon changes weekly using, say 15% distilled water?

Val,

You stated that, "...as someone has already pointed out, consistent parameters are more important than trying to get the parameters to optimal levels for the fish in the tank and risk having fluctuations that could be very stressful for the fish."

Consistent parameters to me indicate that you should use the most consistent source of water to minimize variances in your water. This source is generally tap water. Rams can be particularly touchy about water quality. They appreciate water changes.

I would consider using distilled water in my water changes to soften water only if you are preparing the fish for spawning.

__________
"To steal ideas from one person is plagiarism; to steal from many is research."
researched from Steven Wright

I agree with Bob as well. Rams are very delicate fish who don't like it when something changes and show it quickly enough. You can keep them in your water parameters, but they probably won't spawn. If you do want them to spawn and want to change your parameters, do it before you get the ram and then see your parameters are consistent.

In my opinion, water changes for Rams should be smaller and more frequent. Before having rams I used to change 20% of the water once a week, but they didn't like it and they showed it, so now I change less amount of water more frequently. Even so, you must be gentle with them because doing it too often is not good either. There is a fine line here and you got to find the balance.

It's impossible to tell you exactly how those water changes will affect your parameters, you'll have to try it and see, but please do it without the rams in the tank, this would be too stressful for them. If you are going to do this keep in mind that you will have to test your KH as well, and possibily TDS (depends who you're asking).