I am thinking about adding some livebearers to an outdoor container pond for the summer. I know plenty of people do this, but I was wondering if rain is a problem since especially in heavy downpours a lot of soft water will be added in a short time. Will crushed coral or something like that prevent the gH from dropping too quickly and stressing the fish?

Believe it or not, Melauringa, it rains in a livebearers's natural habitat. I know that sounds sarcastic but I have to tell myself that every time my goodeid summer tub / pond gets a heavy rain. I have decided to ignore any rain that falls on my summer tub except to the extent that I will siphon off some water if the tub gets too full. I have fairly high pH and high KH water that is my first fill in that tub so I don't worry about dilution by rain water. I do change a lot of the water a couple of times during the summer using tap water for the change so I suppose that the KH is taken care of by that change if it was starting to become a problem. Since I seldom do chemical testing on my tub, I don't know if that is valid but I do know the fish look great at the end of summer.

Heck I just 3 weeks ago put some fish out in a container holds about 25 gallons of water since then have had 6 inches of rain fish are doing good I just everyday put in some of my good old hard well water... heck I have not even feed them they are getting plenty of insects I even see a mosqieto in there they missed now and then thanks for letting me put my 2 cents worth in Don

Yes, I do realize it rains in a livebearers natural habitat But I figured the dilution effects of rainwater would have more of an impact in my small tub than a lake or river. I have had probably 6 inches of rain in just the last week. My pH and kH are high too, but gH is low so I increase hardness in my tanks.

It is a fair question. I kept many fish outside last year with no ill effects caused by rain (I don't think). It is obviously cooler in the UK than it is in parts of the US, but the hardier goodeids survived fine outside until the nightime temperatures reached around 9 degrees C when I decided to bring them in.

The only point is that my fish outside needed added food, the natural food they got wasn't enough to sustain them and
I ended up with really beautifully coloured, undersized fish. That resolved itself once I bought them indoors and they have grown on nicely.

yea... rainwater is generally soft and acidic. so keeping up regular partial water changes would be helpful if your tap water is hard and well buffered. You can also increase GH with calcium chloride and magnesium sulfate (epsom salt) and KH with baking soda. That's how the ponders do it. and you're correct, you can add either crushed cuttlebone, crushed coral or crushed oystershell in a mesh bag in a high flow area. Those dissolve over time and increase GH (calcium and magnesium) and KH (bicarbonates) which helps to maintain pH. Tho I've heard folks with bigger ponds probably heavily stocked with koi (who are high on the bioload) talk about the crushed minerals not being able to keep up.

also depending on how full the container is and how much it's raining, you may need to do a bit of draining to avoid it running over.

Water conditions are variable in many habitats, and rain should not have an impact. What does have an impact is the build up of fish wastes and resulting issues.

My 'hot tub' pond raised many generations of many species of livebearer and catfish by being outside without any water issues.

Dear FishFolk,

I put a handful of crushed shell or argonite in each of 50 gallon stock tanks when I set them up each year. I don't put any more in and the daphnia are fine. I've had goldfish in the tubs and now have Black Paradisefish.

Best wishes,

Earl

it depends on how well buffered and hard your source water is and, how much rain, the bioload, how much water you change out etc. for fish that like hard water and alkaline pH, crushed minerals are a good insurance policy. I think crushed shells work better than aragonite cuz shells contain both calcium and magnesium (and magensium is more soluable than is calcium). From memory, I think aragonite is just calcium carbonate.