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jakinthebox 04-19-2013 11:59 PM

Rain Water In Tank- Can I/Should I?
Firstly I'd like to say HELLO :-D to everybody, I am new have never posted before but have already learned loads from the wealth of information here. Something I couldn't find was much information on rain water so I was hoping somebody out there might be able to enlighten me. Here goes....

I am trying to set up a well planted 70g tank, the tank has actually been running for about a year now but only with 3 inhabitants- a 30cm black ghost and a pair of bristlenose. After the initial setup I fell ill for a long time, but am now recovered enough to pick up where I left off. I did some water tests and the tank results were GH 180ppm or 10, PH 7, Nitrite 0, Nitrate 80 I could not get an accurate reading for KH because the strip kept turning 2 colors at the same time (going to get more accurate tests asap). I would like to lower the GH and replicate other more natural conditions for my BG but would rather not use additives if there is another way. Can I use rain water and if not why not?

I live in a very small coastal town, we are surrounded by rainforest and it rains pretty much every day so the rain water tank is constantly overflowing. I tested the rain water which is GH 30ppm or 1.7, KH 0ppm or 2.2, PH 6.0, Nitrite 0, Nitrate 0 and I also plan to take the water to be tested by an analyst. Air pollution here is very minimal but would the water be contaminated by running over the metal roofing? What other risks are there?

On a side note (but still about water), I had to medicate the tank because my BG had a touch of fin rot. The BG is all better now but the water is now a horrible green color :-? the treatment was over 2 weeks ago and I have done some partial water changes but the green color seems as strong as before. How do I get rid of it? Any advise would be much appreciated :lol:

Chesh 04-20-2013 07:19 AM

Welcome to TFK! Sounds like you and your tank are going to be a lot of fun to follow!

People have been using rainwater in tanks for ages, it seems to be something that is often done in areas of the world where the tap water is fairly hard, and pointed to in many of my books as a cheap way to get softer water. I've never done it before, but my guess is that it should be okay.

I would personally have it tested, and I'd try to collect water from an area where it was able to fall directly from the sky into your pail, and not have to run over a roof or even trees, if that's possible. You'll also want to be on the lookout for various bugs and things that you may not want in your tank.

Any chance you can get a picture posted of your green water? My guess is that you may have an algae bloom that isn't being helped by the high level of nitrates/waste in your tank after your illness (glad you're doing better now!). You mentioned wanting to go heavily planted - how much plant life do you currently have in this tank, and how is it doing? Any other algae issues?

I'm still learning, and my research into using rain water stopped very quickly when I found mine to test with a measurable, if low, amount of ammonia *cries* So hopefully someone with a bit more experience will be around with some more solid info for you!

Again, nice to have you on-board, I can't wait to see this tank become what you want!

AbbeysDad 04-20-2013 10:11 AM


I had a very bad experience with rain water that I believe crashed the tank...but I live in the Northeastern US and suspect that acidic rain (and other pollution) did me in.
However, it sounds like you might be in much better shape geographically.

You will have to treat rain water for pH and to add minerals as it will be too pure for aquarium use otherwise because it is naturally distilled water.
(I've used Seachem Neutral Regulator and Alkaline Regulator and Seachem Replenish for minerals [Fresh Trace is another good product]).

As mentioned, make sure your collection is clean. (A roof can collect a lot of evil impurities.) I would also suggest you use/mix rain water 50/50 with good tap (ground) water.

Keep us posted.

Byron 04-20-2013 02:48 PM

I concur with both response posts. I would do the mix, part rainwater, part tap, rather than adding anything. Given the fish mentioned, pure rainwater would not be a problem anyway. This is what I have coming out of my tap, or nearly.


jakinthebox 04-20-2013 11:26 PM

3 Attachment(s)
Thanks so much for your replies guys! I feel better about things now. I'll go and buy HEAPS of buckets to collect directly from the sky rather than using the rain water tank and mix it 50/50 with the tap water. Byron are you saying that if I do this then I don't need to add minerals or anything else or should I still use Replenish at a half dose?

As to the yukky green colour of my tank water I have some good news- its GOING, YIPPEEE! Last night I added Matrix carbon to the canister filter and woke up this morning and the green colour is almost gone! I'm so happy! Check out the before and after photos although the change is much more noticeable in real life, maybe the camera is picking up some green from the plants. The water is still a bit yellow but that's from the driftwood and there were some tannins in the water before the treatment, maybe the carbon will take that away too (fingers crossed). I don't think it was algae (although I do have annoying green spot algae) because when I did the first water changes I made the mistake of pouring it down the bathroom sink which promptly also turned green. I scrubbed and scrubbed to no avail and in the end got the basin back to white by using tons of little alcohol swabs from the medicine cabinet, it took hours :evil: The plants, wood and rocks in the tank are also now a different colour than before.

Tanks for your help:)

Chesh 04-21-2013 09:47 AM

Nice setup, thanks for sharing some pics!
It sounds like you're saying that there is some type of dye in the water? That's very odd! I'll leave that one to our more experienced members, hopefully they'll be able to give you some ideas. Glad to hear it's clearing out now, at any rate.


Originally Posted by jakinthebox (Post 1819329)
Tanks for your help:)

*giggle* Not sure if that was a typo, but it made me smile!

jakinthebox 04-21-2013 11:01 AM

Hi Chershaca,
One of the ingredients in the medication was malachite green and it even says on the bottle that "this is an intensive dyestuff" but I naturally assumed that the colour would go away after a while. Methylene Blue (for fungus) is the same but even worse, so bad in fact that you can't even see if your sick fish is getting any better!

Chesh 04-21-2013 11:15 AM

I've used MG in the past, but I've never seen it turn the water THAT vibrant - or that green. I always see blue, though blue plus tannins would mix to green, lol. While I've noticed it staining plastic/silicone in the tank, have never had an issue with it dying the actual plants or substrate. . . I don't think I had wood or rocks in, though. Perhaps I used a lower dosage? It sounds like you're right, and the green is simply the effect of the meds you were using in the tank. Glad it's clearing up for you - I can tell quite a difference between the two pictures, and I know how sensitive cameras are to picking up greens and yellows from plants and tannins. Hopefully you'll have your pretty tea-stained water back in a few more water changes!

AbbeysDad 04-21-2013 11:25 AM

I'll jump back in to point out that rain water, at least with respect to hardness and pH is like RO or distilled water. By itself it is considered too pure for aquarium use. If your tap water is hard and your pH is high, then adding rain water to it 50/50 is good as it brings these down. On the other hand, I add minerals and adjust pH of the pure water to better match my filtered well water, rather than change it's values.
In my thinking this better ensures a more consistent water chemistry.
As I mentioned, it depends on your tap water chemistry as a 50/50 dilution of tap and rain water (w/o treatment) might well be a good thing.

Byron 04-21-2013 01:54 PM


I'll go and buy HEAPS of buckets to collect directly from the sky rather than using the rain water tank and mix it 50/50 with the tap water. Byron are you saying that if I do this then I don't need to add minerals or anything else or should I still use Replenish at a half dose?
You mentioned soft water fish, the Black Ghost Knifefish and a couple Bristlenose Pleco. These fish, and all soft water fish, do not need any minerals in the water. Live plants do, however.

I have had very soft water for over 20 years. Presently the GH out of the tap is 7 ppm which is less than half of one degree. I've not tested our rainwater, but I suspect it is probably the same. I have to raise the GH to around 5 dGH for the plants in some of the tanks, otherwise they have insufficient calcium and magnesium. Soft water fish do not need any of this, but having some hardness is not going to bother them that much.

In your case, I would dilute the tap water with rainwater. This works proportionally. So if you combine half tap and half rain water, the resulting GH should be half of what the tap is. Since you have mineralized tap water, I would rely on using this to raise the mineral a bit, and not resort to expensive chemical concoctions. In my situation, I use Equilibrium which adds hard mineral sulfates that benefit the plants but have minimal effect on the fish.

Remember that you will need to do the mix for water changes too, to keep things balanced.


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