Frogs

https://www.vimovingcenter.com/talk/read.php?4,146224,151930#msg-151930

If you click on search, type in 'frogs cistern' and all dates you will get this old post and many more.

We used to also have occurence of a frog or two, leaf and other debris in our cisterns. We installed not only UV water filtration system but also Leaf Eaters
http://rainharvesting.com.au/products/pre-filtration/rain-heads/leaf-eater-ultra

Leaf Eaters work great and I would highly recommend them.

I have screens over all of the downspout holes and overflow pipes.
Plus a water filtration system.

The frogs in your cistern go out at night to feed and come back and hide in your cistern during the day because it is a dark moist environment for them. If you chlorinate your cistern, which you should do anyway, they will move out and not come back. You should add 4.5 to 6 ounces of regular unscented bleach per thousand gallons of water in your cistern each month. This recommendation is based on the assumption that the bleach you are using is 5.25% sodium hypochlorite. If you are using concentrated bleach (8.25%) then you you need to reduce the amount you add accordingly. Swimming pools are a good example of how effective chlorine is at keeping frogs at bay. If properly chlorinated you never see any frog eggs or tadpoles in them, only a dead frog every now and then if they jumped in and could not get back out.

Excellent recommendation JE!

Wouldn't adding the bleach for the many thousands of gallons each month really add up concentration wise after a few months and become very strong in taste and odor? - the amount of water that is replaced by rain is usually a small percentage of the total - or does the bleach lose its effectiveness after a month?

The chlorine dissipates, similar to that in a swimming pool. You have to keep adding it to maintain the levels.

Chlorine is a gas that is combined with sodium hydroxide to form sodium hypochlorite, which allows the chlorine to remain in a somewhat stable liquid solution. However, as soon as it is bottled as bleach it begins to breakdown, releasing the chlorine gas which is the sterilization agent. So the salts that are a byproduct of the chemical breakdown will concentrate in the cistern but not the chlorine. Even though you might be adding 60 ounces of bleach to 10,000 gallons of water, over 50 ounces of that bleach is just pure water, so there is not too much other stuff anyway to concentrate relative to the amount of water in the cistern. At any rate, I would also recommend a Ultraviolet Purification System with a charcoal filter be used in conjunction with the bleaching of the cistern. Charcoal is an excellent filtering medium and will remove the vast majority of remaining chlorine and salts in the water.

Disclaimer: I own a company that installs UV Purification Systems

Thanks JE.

By the way, you're making a disclosure, not a disclaimer.

Thanks, you are correct!