Distilled Water to Lower pH/kH

M

MattS

AC Members
Apr 12, 2009
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Hi, there.

Some months ago, my 40-gal tank's chemistry went wild, killing most of my fish. The good folks on this board helped me track down the problem (bad AmQuel) and the tank is now alive again.

During that crisis, the water turned extremely acid, and I used some baking soda to try and save the lives of what fish I could. It helped, but ever since the pH has been very high (off top of scale, I'm guessing 9.0) and the kH also very high (20 drops in my test kit).

It's been several months; the fish seem active and happy, and i've restocked. The plants seem OK, but I think they are not doing as well as they would with somewhat softer water. The leaves tend to tatter and look thin.

I don't want to use any chemical solutions, and I already have driftwood in the tank that's been there for years; I'd rather not replace it. I don't think the substrate is keeping the water hard, because the tank had been around 7.0 pH for years before this recent disaster.

So I've been planning to add some distilled water every couple of weeks and monitor the chemistry carefully. I added about 3 gallons for the first time a couple of weeks ago. Fish and plants seem happy, but the water is still extremely hard. I'm planning to add a few more gallons today.

Good plan? Bad plan? I know that pH doesn't need to be "perfect" if the tank seems happy, but I also would like the plants to thrive.

Thanks!
 
The only downside I can see in your plan is the price of all that distilled water. Especially if the pH and KH rebound to their higher levels.

What kind of substrate do you have in your tank? And what are the KH and GH levels in your tank? If the KH is off the chart, do you have shells or other calcium carbonate sources in your tank? If so, those could be the source of the excess carbonate.
 
It's sand and gravel substrate that's been there since the tank was established about 8 years ago, so I assume it can't be that. In the past I've had small pieces of coral in the tank for buffer, but there is none in there now. kH at 20 drops is off the top of my test kit, which tops out at 214.8 ppm.

I strongly suspect the high kH and pH are from the baking soda I added in a panic when my tank crashed (though it did save some of the fish).
 
What are the parameters of the water out of the tap? You said the PH is normally around 7, so I am guessing your source water is not that hard. If that's the case, I'm at a loss why the PH would still be near 9 after all this time.
 
The tap pH is high, at least 8.0, and the kH is about 125 ppm.

In the past (Before Crisis -- BC) the tank maintained 7.0 very well, but I was a Bad Aquarist back then and didn't track kH.

It can't have been all that high, however, since I know that if I didn't keep a piece of coral in there the water would tend to become acidic in between water changes.
 
I don't see any harm in mixing in more distilled /RO untill the KH drops down to 125ppm. I'm surprised that normal water changes have not brought it down more.
 
Thanks, Gregg. Yeah, I was surprised too -- that's why I waited months before considering distilled water. I generally find that the less I muck around with water chemistry, the happier everybody is.

Very early in the hobby, I remember trying desperately to get the chemistry on a 20-gallon tank just right, constantly changing water, tinkering with chemicals, adding and subtracting coral. Finally I got frustrated and just said the heck with it, stopped doing anything at all and figured everything would die.

Instead, within a few weeks, the tank stabilized. Since then, I've tended to just let sleeping fish lie, as it were.

Until this recent crash, all I ever did with my current tank was change about 20% of water and replace filter and charcoal each month, with the occasional top-off, and it stayed just fine.
 
The most baking soda can raise pH is 8.2 or 8.4 so if your pH is above that you have something else funky in your water (I'd suspect your test kit is wrong?). How long has this tank been set up? Not to insult you but 20% water change a month is not going to be adequate for maintenance of a tank unless it's really lightly stocked with fish and has lots of plants. Your description of your crisis sounds alot like a tank that has crashed due to build up of organic acids and exhaustion of carbonate buffer.

Anyway, distilled water can be used to soften water. I'd suggest monitoring the kH of your tank closely and would probably use distilled water mixed with tap. And increase the frequency of changes to bring your kH down more.
 
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Yeah, definitely go with the distilled water. It sounds like you've got an excess of sodium to bicarb in the tank. The sodium will raise the pH as the bicarb is depleted, so a pH of 9.0 is well within the realm of possibility, and with a kH of 125 out of the tap, you don't need much additional HCO3 hanging around to send the kH off the chart.

Are you using well water?
 
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