Advice please - Rain water harvesting for ponds

[bob1]

Hi all, my first post

I am planning a new pond and decided to set up a rain water harvesting system for filling and topping up as well as general garden watering. Seemed like a good idea at the time….

I have two closed IBC 1000 litre tanks connected together which collect the water from the gutters on the metal workshop roof. (Some trees above though).
Both containers were full after a month or so and all looked good. Recently though - late summer before the leaves started falling - I noticed the water had gone a dark colour and smelled stagnant.
After some thought I installed a circulation pump and a UV pumping from one tank through the UV into the other tank and back via a 2” permanent syphon. This works fine flow wise but after six weeks there is no change to the water.

I spoke to my local pond emporium yesterday and they told me that I shouldn’t store or use rain water for pond use. This is because rain water is too soft and minerals are required to be in the water to stabilise the PH and for general fish health. Also stored water is bad because of bacteria growth and the UV will not help kill these types of bacteria. Also I shouldn’t even use the water for watering vegetables and flowers because I will use a spray and this will release legionella into the air which is dangerous. Their advice is to use tap water and add chemicals to remove move the chlorine.

So - my question(s),
is any/all of this true?
Are they just trying to sell me chemicals?
Should I abandon my water saving idea?

I feel rather fed up now after the work and expense of the water harvesting system. Thought I was doing good, but perhaps I should have researched this more before I started.

The planned pond will be 2.4M x 1.8M with about 400mm above ground and 900mm dug out. Planning ornamental sort of thing with some planting and a few goldfish etc. No Koi.

Any comments or ideas welcome.

Thanks for reading

 

[j.w]

@bob1
The only rain water my pond gets is what falls from the sky or what's from our well when it needs topping off due to evaporation. Some here use it from off their roofs etc. Maybe they will be of more help.

 

[JRS]

Welcome to the forum. I let roof water drain into my pond but I do not store it. I have very hard water and the rain water helps counteract that, especially after a lot of evaporation.

Lots of folks in my area use rain barrels; have not heard anything much about Legionella although warm temps appear to be a contributing cause in addition to stagnation. Looks like there is a possibility but depends how careful you want to be and take steps to mitigate the risk.

Lots of different bacteria and pathogens associated with water. I even suspect I may have had a mycobacterium infection in a finger cut after squeezing an aquarium filter sponge to clean it. Culture was inconclusive but the appropriate antibiotic finally killed it. Now I make sure to wear gloves just in case.

Legionella risk in your garden - should you be worried?

Can gardening equipment harbour Legionella i.e compost, waterbutts, hosepipes? and how can you reduce the risk of Legionella in your garden?

www.waterhygienecentre.com

How To Clean A Rain Barrel

www.aquabarrel.com

How Legionella Spreads

These bacteria spread through water systems and devices.

www.cdc.gov

 

[permaculturebob]

Your reference to legionella inspired me to do some research, since I rarely consider those sorts of less prevalent (to me) concerns. But then I get regular exposure to all sorts of random potential sources of pathogens and count on a healthy immune system.

In general associate pathogens with anaerobic conditions, healthy bacteria with oxygen.
Another purifier is sunlight, not as much with irradiation to kill bacteria, more in the sense of allowing an algae film to develop on the sides and bottom of the tank. with enough light you will encourage a self filtering water storage that removes nutrien from the water about as fast as it can enter (pigeon poop etc)

As far as the minerals, that.s not really a worry, after the pond is full and you're just topping off everything will rebalance pretty quickly, and even if you fill it completely with rain water, and even if the rain water were completely deionized/ distilled,

Now we get to the fun(possibly most relevant) part, tanins in leaves--here's what grok had to say.

"Tannins leached from leaves into rainwater (especially in forested or leaf-litter-rich areas) generally inhibit Legionella growth in natural aquatic systems, acting as a natural bacteriostatic or bactericidal agent at environmentally relevant concentrations." insert multiple properties of tanins here- and the short answer

"So yes — that brown, tea-colored water in the woods? It’s nature’s Legionella shield."

Further talks with grok indicated a high tolerance for natural tanins in fish, and beneficial effects of using them.

all that being said, you didn't seem as concerned about the condition of the metal roof, so I assume it's not prone to possible inorganic contamination. Most intact well maintained roofs should be ok with the dilution factor, but if it's not brand new, or getting fresh deposits from activities in the shop (exhaust fans/ smokestacks, that should be fine.

 

[Hopalong]

Have you tested your rain water??
If you are near an area of industry you may find chlorine present, also that the ph of the rain water may also be different to your tap water.

 

[jdale]

If you are removing water from the pond and replacing it with rainwater (i.e., water changes), then you'll be losing mineral content, the water will get softer and more acidic. In that case you might need to add hardness and alkalinity.

If water is evaporating and you are just topping it off as needed, all the mineral content remains in the pond and the dilution level is only going up and down a little bit. The mineral content won't evaporate away with the water.

I get enough rain that water washes out and my mineral content starts to drop. I got behind on that and ended up having to add quite a bit. You can use additives intended for a pond, but it's cheaper to use baking soda and lime. Just go slow and test the water so you don't overdo it.

 

[GBBUDD]

I have a 3000 gallon cistern, and have been using it in the pond for 6 years now.
I collect rain water from one whole side of the house. So it adds up. Add a heavy down pour and it can be an issue for a ph crash if the KH is not monitored or kept at a good level.
But here's the difference in your application to mine.
My rain water goes directly to the pond. The pond has a overflow where the last intake from the pump is and as it draws its 8000 gph any extra amount say from a rain event will over flow that containment. That over flow drops into my storage area being my cistern. Here is the biggest difference though I run a 2000 gph pump in the cistern it could be much smaller. That pushes the cistern water back into the pond constantly thus no stagnet water no nasty algae, or build up of nasty bacteria, parasites and even mosquitos. Again all this water from the 2000 gph pump over flows the last collection area of the pond and it drops into the cistern.

The water level in the cistern is the only area where water drops in my set up. That is unless the cistern runs dry. But on average I add 1000 gallons from the tap twice a year. As the rains may get behind d.

So as long as I monitor my kh levels I dont have worries about ph crash from acid rain. This can and has cost me a fish or two until I got use to the setup I had as much yo learn about the pond in use as I did in building it.

 

[j.w]

@Go fish

 

[sissy]

I use lots of rain barrels but with a shingle roof on the house it is dirty . But on the sheds with metal roof it is somewhat better but do not use it in my pond