# Rainwater confussion



## idris (27 Feb 2021)

Our tap water is off-the-test-chart hard. Literally. GH>180 and KH >240 with a pH around 7.2
Our rain water is GH<40 and KH<30 with a pH of 6.3

I've never bothered with rainwater before and have no species related preference (fauna or flora), but was wondering about using rainwater in my low tech tank.
I know some very knowledgable people use 100% rainwater, and some us 50/50, but after reading quite a few threads, I'm entirely unconvineced what difference it would make, positive or negative, if I did.
Any thoughts would be welcome.


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## shangman (27 Feb 2021)

I use 90% rainwater in my tanks, as do some others here. The 10% tap is just during the winter to warm up the water quicker. I'm sure @dw1305 knows much more about this.

I personally use the rainwater for 4 reasons (I also live in a hard water area). No 1 is because I like soft water fish which are healthier, live longer and breed in soft water. The second is that some plants prefer soft water, so I can grow a few more plants lowtech without co2. A third reason is that my rainwater gets insects living in it which the fish love to eat (daphnia, moina, seed shrimp, ostracods, mosquito larvae) so they get a good regular live food feeding with their water change, 2 birds one stone (I have some extra waterbutts for more food too). A fourth reason is none of my equipment gets limescale.

A fifth reason - which had no scientific backing at all - is that it feels more natural to me, though it is more hassle to change the water.

I have a nano tank with shrimps and snails where I just use tapwater and it seems to work just as well with lots of thriving life and plants, I would mostly be led by what your favourite fish needs are.


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## Nathanh2150 (27 Feb 2021)

Iv just recently had a water butt installed to the side of my property and was also thinking the same to use rain water in my aquarium as I also have hard water. I was thinking of adding the rain water into a bucket and add a heater to get it to the temperature of my aquarium I do 50% water changes each week and top the tank up daily as I have an open top tank would I also need to add tap safe to the rain water also beneficial bacteria? What’s everyone’s thoughts on doing this ?


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## ScareCrow (27 Feb 2021)

Factors like where you live, what your roof is made of along with many others, will all have implications on the parameters of your rainwater. I've used 50:50 (rainwater:tap) up to 100% rainwater. I don't know what the alkalinity of my rainwater is but it has a TDS of around 60ppm, compared to 300+ppm from my tap. The reason for mixing is generally so you can add some alkalinity back into the rainwater and get your TDS of preference.
You don't need to add anything if you're just using rainwater. If you're using a mix then treat the tap water as you would do normally.


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## Aqua sobriquet (27 Feb 2021)

I use about 90% Rainwater mixed with hot tap. Virtually gone are the calcium deposits I used to get on the glass and equipment.


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## Conort2 (27 Feb 2021)

idris said:


> Our tap water is off-the-test-chart hard. Literally. GH>180 and KH >240 with a pH around 7.2
> Our rain water is GH<40 and KH<30 with a pH of 6.3
> 
> I've never bothered with rainwater before and have no species related preference (fauna or flora), but was wondering about using rainwater in my low tech tank.
> ...


What species of fish do you keep? Some will thrive with rainwater. For others it can actually be detrimental.

Cheers


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## idris (27 Feb 2021)

Conort2 said:


> What species of fish do you keep? Some will thrive with rainwater. For others it can actually be detrimental.
> 
> Cheers


At the moment just some Neons, a couple of Kuhlis, a small plec (not sure what varaiety - it was donated), a single Amano and some Assasin snails. 
I know the shrimp and the snails will like hard water, but I'm not really tied to other species.


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## Paulus (28 Feb 2021)

Fitted a 227 liter rain barrel last week. I wanted to try this again instead of the tap water.
Also want to try if i could get the TDS around 120 for better plant grow etc
Current TDS values:

Tap Water: ±175
Rain water: ±14
Still trying to find a good and simple solution to fill the aquarium with the rain water in this period of time cause the water outside is around 8C. Pretty cold.
So today i did a first "little" water change with the rain water using 3 old plastic jerrycans i still have of 20 liter each.
Couple days ago i filled the jerrycans and put them inside to get them on room temperature and for use this weekend. Don't want a separate heater for this 

During the filling of the jerrycans i used a cut of PET bottle to create a simple funnel. Inside it i put some leftover white filter floss to try/keep large "waste" out of the jerrycan.
Now i also put some white filter floss on the inside of the barrel intake to see if that will work. (also ordered a simple filter sock to see if i can use that on the intake. Something they use for prefilters in ponds/koi).

Only "downside" of the jerrycans now is the filling of the tank. Or you need to lift it and put the water in the tank (and get a free workout) or put it on a higher position and let gravity do the job.
Oh and i could only change 60 liter now so i still had to use tapwater for the rest. So TDS in the tank is still bit higher now. SO maybe it will need more water changes over time (or summer so i can put a pump in the rain barrel when the water is not so cold).


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## tam (1 Mar 2021)

You can get pumps for the cans, might be called caravan pumps or similar. They are small cylinder shaped. Or use lidded buckets instead of the can. I use too hot tap water to sort the temperature. Same as you cut the tap with rain to lower the TDS, start with the tap too hot so when you cut it with the colder rain it ends up at the right temperature.


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## idris (1 Mar 2021)

How to pump from a water butt is useful to know (I think the caravan pumps you're talking about are made by Whale - I used to use them for water changes), but doesnt really help me know whether I should be using rain water or not 🤣🤣🤣.

What are the down sides to using rain water (fish species notwithstanding)?


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## Kezzab (1 Mar 2021)

Apart from the faff and hassle I dont think there are any. Less 'stuff' in the water means a blank slate and you can be more certain about what is in your water because you will have put it there.


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## timdjones10 (16 Mar 2021)

I always bring my rain water inside and run a filter with carbon in it for 24hrs before putting in the tank to make sure any potential pollutants are removed


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## dw1305 (16 Mar 2021)

Hi all,


idris said:


> What are the down sides to using rain water



It doesn't rain reliably in the summer so you need more storage than you might imagine. 
You need to warm it up in the winter, if you want to change more than~10% volume.
It can freeze in the butt if it is prolonged cold spell.
Other than that it is all "up sides",

Free
Environmentally sustainable
Low conductivity
Doesn't contain chlorine
or sodium hydroxide (NaOH)
or orthophosphate (PO4---)
cheers Darrel


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## idris (16 Mar 2021)

How about BGA? I've had an outbreak since switching to it, but as the butt has a lid (ie no photosynthesis) and there are other possible causes, I'm assuming it's not the culprit


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## Paulus (31 Mar 2021)

Other question: when using RO or rainwater etc and you want to add minerals to it you have these GH/KH products.
But is there a difference between GH+ for aquarium and Ponds? Or can you also use for example Velda GH+ in your aquarium to add the minerals?


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## dw1305 (31 Mar 2021)

Hi all, 


Paulus said:


> Or can you also use for example Velda GH+ in your aquarium to add the minerals?


You could. You don't need anywhere near the 8 -12 dKH <"they suggest">. 

Because magnesium sulphate heptahydrate (MgSO4.7H2O) "Epsom Salts" and calcium chloride dihydrate (CaCl2.2CO2) are so cheap (and widely available as "food grade") anyway I would use them.  The workings for a DIY mix are at <"James' Planted Tank">.

Have a look at @Roland 's comments in <"RO, re-mineralizers and pH">. 

cheers Darrel


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## jaypeecee (31 Mar 2021)

idris said:


> How about BGA? I've had an outbreak since switching to it, but as the butt has a lid (ie no photosynthesis) and there are other possible causes, I'm assuming it's not the culprit


Hi @idris 

Some species of Cyanobacteria (aka BGA) can survive in a dormant state - known as akinetes - until favourable conditions return. They've been around for 3.5 billion years so they are well-equipped to handle less-than-ideal conditions. But that's not to say that they can't be controlled/eliminated. That's why they've been such a source of fascination (and a challenge) to me because of what they can do in our tanks.

JPC


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## jaypeecee (31 Mar 2021)

Hi @idris 

You may be interested to read this:









						Bacteria and Algae Hitch a Ride in Clouds
					

Human health and ecosystems could be affected by microbes including cyanobacteria and algae that hitch rides in clouds and enter soil, lakes, oceans and other environments when it rains, according to a recent study.




					www.technologynetworks.com
				




JPC


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