Rainwater and its use in aquaria If the cost and environmental impact of a reverse-osmosis filter doesn’t appeal, then collecting rainwater may be an attractive alternative. Setting up a rainwater collection system is inexpensive. The 200-litre rainwater butt cost about £30, and installation involved little more than cleaning out the gutters, cutting the downpipe to size, and fitting the downpipe to the water butt. Is it safe? Yes! Unless you live somewhere with serious air pollution, rainwater is likely to be at least as safe to your fish as tap water. It will contain no nitrate and no copper, both of which are common problems with tap water. Apart from air pollution, there are three issues that need to be considered. The first is the cleanliness of your roof and gutters. Regular slates and tiles won't harm rainwater (after all, both slate and terracotta are widely used in aquaria) but tar and plastic could be less safe. These might leach chemicals into the water that could be toxic fish. Secondly, the water butt itself needs to be clean. You will be staggered how quickly things like leaves and dead insects accumulate in your rainwater butt! It’s a good idea to clean out the water butt every couple of months. Finally, you need to be able to collect and store rainwater reliably enough that you always have some to hand for necessary water changes. Reliability and storage Here in England, rainwater is generally something that falls from the sky with depressing regularity! But elsewhere the story might be different. Balance the rainfall in your area against the demands on the aquaria you have in terms of water changes. There’s not much point using rainwater if it is only viable for a few months per year. Rainwater can be easily stored in buckets with lids. I use 5-gallon buckets picked up for under £5 at a home decorating store. Treating rainwater It is a good idea to filter rainwater through carbon. A box filter filled with carbon and run using an air pump will do the trick nicely. Whether or not carbon will make any difference is unknown; after all, carbon only removes organic compounds and iodine, and will have no affect on dust and other inorganic pollutants. Adding dechlorinator is not strictly necessary, but won’t do any harm, and may do some good. Use in community tanks For my community tanks, a 50/50 mix of rainwater and hard water is about right. This will produces water with a general hardness of about 10 degrees dH and a pH of about 7.5. But the precise ratio needed will depend on your own local water conditions and the species being kept. Use a test kit to determine the general hardness of your local water supply, and then compare the result against the general hardness you want for your fish. If your intention is to maintain soft water fish species, then a Pearson’s Square can be used to calculate the precise ratio of rainwater to tap water required. To that end, I’ve written a Mac/Windows application called Soft Water Ware that does this job. If your aim is nitrate-free rather than soft water, then adding a suitable mineral salt mix will be necessary. You can buy these ready made, but you can also mix your own. A typical Rift Valley cichlid salt mix suitable for Malawian, Tanganyikan and Central American cichlids is as follows: Per 5 gallons/20 litres * 1 teaspoon baking soda (sodium bicarbonate) Note the proportions of the different minerals; simply adding salt (even aquarium salt) by itself won’t turn rainwater into water suitable for freshwater fish! It may be possible to use marine salt mix by itself to create brackish water though. This approach could be used for those types of fish that require such conditions, including of course brackish water fish but also certain livebearers tolerant of brackish water, notably guppies, mollies and Limia species. |
Rainwater butt in situ
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