Rain water

If you do water changes with mature rain water that has had a ph crash the aquarium ph will go down, but if you do water thanges with rain water that hasnt had a ph crash then the aquarium ph probably wont crash? This confuses me.

 

Hi Mitchell.

I'm not sure I'm understanding your post too well, but let me try and explain, and hope I'm right.....

Rain water, being pure evaporated water (if we exclude the potential for pollution), should be at pH 7 as it would contain no other chemicals or substances at all which would affect the pH.

Now, since the water contains no hardness, since there is no Ca or Mg in there, this leaves the pure rain water with absolutely no buffering capacity. When you then go and add this to your aquarium, the chemicals in your water (mostly from decomposing waste, and the nitrogen cycle, etc) will cause the pH to drop because nothing can stop it due to a lack of the Calcium (Ca) and Magnessium (Mg). If the water had flowed through a river or through the ground to become our 'table water', then it will have disolved several minerals into it along the way, which is where the buffering materials come from. Sometimes the water treatment facility needs to add a buffer to lift the pH and hardness to help stop the water from corroding the piping, but this is usually only in areas where the water is very soft, and lacks these minerals.

So, to try and make sense, add rain water to your aquarium, and over a short period of time (could be days, could be weeks, depending on how much you added, and the stocking of your tank) the pH will drop. This is regardless of whether the water has aged or not. This can be controlled if mixed with tap water, and can assist in lowering the hardness and pH if you are in a hard water area. In a soft water area, you would need to add a buffer to stabilise your pH, but this has to be done carefully, as too much buffer (which is effectively just adding hardness to the water) will have the opposite effect, and you can end up with the pH increasing.

Unfortunately, this can be complicated by pollution. This can make the 'pure' rainwater acidic, as the water in the air has dissolved some of the chemicals that have entered the air from industry, car fumes, etc. This then complicates matters, and is the reason why it is suggested that you don't collect the rainwater until it has rained a good while. That way, some of the pollution will have cleared the atmosphere. This is why the air always feels fresher after a good rain or thunder storm.

Hope that helps?
Regards
G!

 

@Big G nice explanation, thanks

 

Guys, it simply does not make sense using rain water.

One, it is inconsistant. When you do not have rain water, you must use something else, meaning you are changing you consistency.

Two: pH buffer problem. (Same as RO water. Tap water or salts are to be mixed in)

Three: Rain water contain ammonia. Google it. The text book say rain water contains minute quantities of ammonia, less than 0.5 mg/l. Now, that is not so minute as it seems. 0.5 mg/l at 27 deg Celsius, 200 tds, 8pH, translate to 0.0284 mg/l un-ionized ammonia (mg/l) Now, we know that from 0.02 mg/l, un-ionized ammonia-N start to have a long term toxic effect on our fish and from 0.4 mg/l things get very toxic. So, it just do not make sense to add ammonia to your tank. OK, granted, you will not have a 8pH if using rain water, more like 7pH, where the amount is one eight of what is toxic. But that is an eight wasted!

Four: Other impurities. You are probably collecting from the roof, to get sufficient volume. You have no idea what is collecting up there. Playground for doves, birds, rats and what not!

Therefore, RO water is the better choice. No ammonia, clean and consistent. The same recipe, time after time.

I lost a dear friend, Chuck the goldfish and I am convinced it stems from me using rain water. Whether it was ammonia, pH shock or disease, I do not know. Point is, I lost him.

 

@Tom.K just out of interest, does tap water contain ammonia or lower levels than rain water?

Sorry I havent tested mine as I am in the process of getting test kit (Hell im in the process of getting alot of things I think I should consider starting an lfs - just kidding)

 

@jwalker

Klerksdorp tap water:
8.94pH
0.00 Total ammonia nitrogen (mg/l)
17.9 gH (318 TDS)
-104.5 mV
0.08 PO4 (ppm)
0.15 Fe (ppm)

Zero ammonia means if there is ammonia present, it is too small for my equipment to register. I measured it an hour later as well and it still read 0.00, so the chances is that it is zero.

 

WOW your gH is hard. Are you softening your water at all?

 

Yes!
130lt RO
110 lt Tap

 

Yep.. that would probably bring you down to 8?

 

yip, that is what I aim for. pH however still near 8 then. So, with my WC I brought it down slowly to around 7pH and 6 - 6.7 gH

 

@Tom.K, thanks for the info, much appreciated!