# Rainwater's pH KG and GH. Opinion please



## NursePlaty (Mar 24, 2010)

My rainwater's pH is 6.4 and I believe both my GH and KH is 1st or 2nd degree or 17.9ppm-35.8ppm. Hard to tell with only 1 drop in a 5ml tube because the color is so faint. 

I am trying to lower the hardness of my water to achieve soft water. Is rainwater safe to use? I am not sure because of the low KH, it I think it might make the pH fluctuate rapidly and etc, IF IT DOES THAT, dont know if it will. im not sure.. Not sure if I am making sense. Need someone with a full understanding of this to help me


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## TAB (Feb 7, 2009)

Rain water can be good or bad, my $.02, don't use it.


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## Diana K (Dec 20, 2007)

What are the test results for your tap water?
GH, KH and pH?

Then make some sample mixes:
25% Rain + 75% tap
50/50
75% Rain + 25% tap

Here are my ideas:
Rain ought to have 0 degrees GH and KH. If there is a lot of dust in the air there may be TINY bits of minerals in the rain water, but really almost none. 
pH may be really low with carbon dioxide. 

By mixing rain with your tap water a 50/50 mix will cut the GH and KH of the tap water in half. (Given that the rain really is 0 degrees each)
With 75% rain the mix will show only 25% of the GH and KH of the original tap water. 
If you used only 25% rain + 75% tap then the GH and KH of the mix will be about 75% of straight tap water. 

If the rain really does have traces of minerals in it, then the numbers will be a tiny bit higher, a difference probably not testable with most kits available to the hobbyist. 

If you set out a bucket of rain water I think the pH will rise to pretty close to neutral overnight. 

Rain water may very well be safe in the aquariums. I use it every winter. I am near some petroleum processing plants, but not directly down wind. 

To test smaller values:
Start with twice as big a sample. The AP tests for example start with 5 ml of water and 1 drop of reagent = 1 German degree of hardness. If you start with 10 ml, then 1 drop = .5 German degrees of hardness. carrying it any further is not warranted. It is not that accurate.


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## NursePlaty (Mar 24, 2010)

I meant to say the rainwater's GH and KH is either 1-2d not my aquarium water. It even mightve been 0.



TAB said:


> Rain water can be good or bad, my $.02, don't use it.


I understand where you are coming from and that it is risky, that is why I wanted to make sure by asking all the forums that I ma in just to make sure.

and DianaK
My AQUARIUM ph is 6.8 or 7.0 because of the injection of pressurized CO2. If there isnt CO2 being injected, I believe the pH is around 7.6. My KH is degree 5 or 89.5ppm. My GH is too hard to read because the API GH test kit's too faint in color but i THINK it is at degree 6 or 7 or 107.4-125.3ppm.

Because of the KH of the rainwater is so low, wouldnt you be worried about the pH fluctuating so much? And might causing a high or low pH spike?


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## Diana K (Dec 20, 2007)

Mixing rain water with your tap to refill the tank after a water change is not a problem, and is a good way to make the water softer. You are not filling the tank with pure rain water. 
Topping off with rain water to replace evaporated water is better than tap water. The minerals that were left behind when the tank water evaporated are still in the tank. Better not to add more minerals, just replace the evaporated water. 
What better to do this with than rain water? Think about it: Rain water IS evaporated water! Just like the water the tank has lost! (Unless you are downwind of some particularly bad factory or chemical plant- then I would not use rain water.)

When you do a water change using rain water + tap water the KH and GH of the final mix will be intermediate between the tap and the rain water, per my comments above. You will not do a sudden all-at-one-go sort of a change. That could shock the fish and kill them. 
Test the possible mixes as I suggested above- some rain water + some tap water. 
If you will be doing a large water change, then use less rain water (Perhaps 25% rain + 75% tap) for a few water changes to start acclimating the fish to the new water. (1-2 water changes per week for 3-4 water changes)
After a few like that, go to a few water changes with 50/50. 
It may take a month or two to alter the tank water to half the current GH and KH. That is OK, that is easiest on the fish. 

What is your goal? What GH and KH do you want the tank to end up at? 

KH of 5 degrees and GH of 6-7 degrees is fine for most of the fish and plants that we keep. If you are planning on breeding some really soft water fish (Rams, cardinals, Discus...) then you would probably end up setting up a tank that might be 75% rain water + 25% tap and the GH and KH would be no higher than 3 degrees, with peat filtration if the species needed it. 
Even at 2-3 degrees KH the pH an be stable enough, unless there is something else going on to alter it. 

Fish can handle the daily fluctuations in pH that is standard in a planted tank. 

Recap:
Fish DO NOT NEED stable pH so much as they need stable mineral levels. Keep the GH and KH where the fish are fine, or alter these levels very slowly, and it does not matter what the pH does. When the GH and KH are stable the pH may change as much as a whole unit (from 6.5 to 7.5 and back again, for example) in a daily cycle and the fish are fine with that. 
Note that the farther away from neutral the pH is the larger the change actually is between 2 units. However, at the typical pH of our tanks (most planted tanks that I hear about have a pH between 6.0 to 8.0) the variations are fine for most of the fish commonly kept. The minerals in the water at as a buffer, stabilizing the pH around a particular range. Other things such as carbon dioxide and peat moss play a part, too, and that is just fine with the fish. 

I also find the GH test kit a difficult color change to see, and it gets worse as the kit ages. I think I will look for a different brand and see if it makes a difference. 
I can read the dip stick test strips easier. They do not always make sense, though. They occasionally turn colors that are not on the chart.


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## NursePlaty (Mar 24, 2010)

That makes sense. I might even do 75% RW or RO water mixed with tap water to make it soft. The reason why I want to make it soft and slightly acidic is for my crystal red shrimps. Im happier knowing they are more comfortable in the water parameters they prefer to be in. 

I dont know what my GH is currently at. They said it should change from orange to green. My first drop is slightly yellow orange, 2nd drop, a more distinct slightly yellow orange. 3rd or 4th or 5th drop and on I see a TINY bit of green. As I go on even further it doesnt get dark green it stays a light green. At the beginning on the drops, it's so little that its hard to differentiate because its half orange half green and my test kit is fairly new. 

I want both my GH and KH to be 3-6 degree I guess. Whatever is suitable for acidic fish such as discus, angel fish, tetras, Crystal red shrimps.

I will never go back to test strips, it's so inaccurate that it drives me insane. Makes me think the hardness slot is inaccurate also.


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## HeyPK (Jan 23, 2004)

I use rainwater because my tapwater has a KH of around 10 and a GH of 0. It apparently has a lot of sodium bicarbonate in it, but no calcium or magnesium. The high KH just means that it is harder to get calcium and magnesium in the water from limestone, egg shells, clam shells, etc.

I once did a 100% water change with aged tapwater in a 15 gallon tank. I had some Ceratophyllum in the tank, and within two days it showed serious calcium deficiency, with the growing tips turning white and dropping off. I added a quarter teaspoon full of slaked lime [Ca(OH)2] along with CO2 to keep the pH from going up and to dissolve the lime, and in two more days the plant recovered from the deficiency symptoms.

I thought, "Who needs all this sodium bicarbonate in the water? It doesn't supply any needed nutrients to the plants." So I started collecting rainwater. I add some ground limestone to my tanks, and this supplies calcium up to around 100 ppm according to my test kit. The dissolved limestone takes care of both KH and GH. I also add a mixture of KCl and MgSO4 and a micronutrient mix and iron DTPA, and N and P in small amounts as needed, and my fish and plants have always done well.

My house does not have rain gutters and drain spouts, and so I place a small plastic child's swimming pool where there is a V in the roof and I can collect around 30 gallons during a typical afternoon thundershower. I don't let the water stand in the swimming pool long enough for mosquito larvae to mature, and I always dump it out before mosquito larvae get to the pupa stage. When I collect water, I filter it with a fine mesh screen to take out any little mosquito larvae that could grow to maturity in tanks that don't have fish.


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## wet (Nov 24, 2008)

Excellent thread and posts.


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## gpodio (Feb 4, 2004)

That's some odd tap water you have there HeyPK! Must create all sorts of problems for people in your area who don't test GH...

As others mentioned, rain water "should" be pure, it's distilled (evaporated) in origin. Anything it has in it was collected from the atmosphere and the surfaces it falls on.

"acid rain" is caused by several conditions which vary greatly between rain falls. Lightning is one of the key causes of acid rain as nitrous oxide is produced during a lighting storm. Other pollutants such as nitric oxide, sulfur dioxide, CO2 and ammonia all contribute to the acidity of rainwater.

Mineral content in rainwater is usually not a good sign as this is not something it collects from the atmosphere, instead it is usually a result of the acidity of the water and the surface it falls on. Roof shingles, concrete and everything else it comes into contact with can add to the mineral content of the water. This is perhaps a greater variable than what's in the atmosphere itself. Some shingles for example have anti-mold and mildue coatings that could leach into acidic rainwater.

Take a look at the following chart, this is a comparison of rainwater samples and some of the materials it comes into contact with:









Source: http://www.uoregon.edu/~hof/S01havestingrain/data.html

So in theory, rainwater that falls on a shingle roof during a thunder storm should be at it's worst...

Regards,
Giancarlo Podio


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## timwag2001 (Apr 15, 2009)

i use ro water and replenish it with calcium carbonate and magnesium. and i use rain water all the time, whatever i can collect. my tanks have fish and plants that typically come from softwater. if i were to keep african cichlids the story would be a little different.

i dont know why people are so scared to collect rain water. every pond and river in the world gets rained on. and when it rains it often encourages breeding.


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