Today Keith is going to talk to us about water, not as simple as it sounds!
Keith Jackson is a retired engineer who has been keeping tropical fish for 40 years and a pond for 11. His first love is the South American family of small catfishes of the group Corydoradinae, covering the genera Corydoras, Brochis, Scleromystax and Aspidoras.
Is there anything sillier than reminding fish-keepers that their fish live in water? Jackson’s cracking up, you say (and you won’t be the first) but it’s worth remembering this somewhat obvious fact and considering its implications for our pets.
What we think of as water, that clear liquid coming from our taps, has been treated and purified before reaching us to make sure that it is safe for us humans to drink but what’s safe for us isn’t necessarily safe for our fishy companions for quite a number of reasons.
In an earlier blog I mentioned the nitrate cycle and said that it functions through several types of bacteria. Tap-water is made to be hostile to bacteria, by the use of chlorine or, more recently, chloramine, and adding water straight from the tap is likely to damage the bacterial population of the filter, potentially leaving too few bacteria to complete the nitrate cycle and stressing the fish. There are many brands of de-chlorinator available from aquatic shops and I’d recommend their use. As I change hundreds of gallons a week in my pond and fish house, I use a commercial carbon filter that fits onto a tap using standard hose fittings but the effect is the same.
That is an important factor but it’s far from the only thing we have to consider. Our fish come from all over the world and the freshwater fish most of us keep – marine fishkeeping is another matter entirely – have evolved to live in an extremely wide range of environments. I’m not thinking of the difference between lakes and rivers but between the rocks over which those waters flow. Some of the rocks in South America are very old and any soluble material has long gone so the more-or-less pure water that fell as rain is in much the same state hundreds of miles downstream. This is water that is very, very soft so its pH – acidity and alkalinity – is easily changed. Passing through some of the most fertile forests in the world means that vegetation falls into the water all the time and, as it rots, it makes the water acidic.
This is the type of water that is home to two species of the Discus cichlid: Symphysodon discus and Symphysodon aequifasciata. They are extremely beautiful, even in the wild forms that are rarely seen these days, and large discus are a true sight to behold but they can be a nightmare to keep. They just cannot deal with even medium-hard water so fish-keepers need to provide not only a large tank – these are almost circular fish that can grow to more than 6 inches/150mm across and need to be in a shoal – but also the soft water they need to thrive. It is possible to strip salts from tap-water using resins, though not conventional water softeners, but the trend these days is to use a reverse osmosis kit. If you’re on a water meter, my advice is to forget discus. It’ll cost you an arm and a leg to buy and run an R-O kit!
At the opposite extreme are another family of cichlids that come from the Rift Valley lakes in Africa, such as Lakes Nyassa and Tanganyika. Here the water is so hard you could almost make bricks from it. Again, water from the tap is quite unsuitable and where you have to remove salts for discus and make the water acid, for these fish you have to add salts and make the water strongly alkaline. Do that and you will have a display of fish with amazing colours but don’t and they’ll simply sicken and die.
Luckily for us, most fish offered for sale don’t need such extreme conditions and will survive quite well with a medium hardness and a pH between 6.5 and 7.5. Breeding may be a different matter but they will live happily enough.
You knew there was a ‘but’ on the way, didn’t you?
Although most fish can tolerate hardness and pH levels rather different from their waters of origin what they can’t withstand are rapid changes, especially in pH. That’s because they don’t live in air.
Jackson’s gone bonkers again!
No he hasn’t. One of the adaptations that allowed our distant ancestors to leave the water behind was the evolution of a skin that was impermeable so that our internal water stays there. As a result, we don’t dry out, as amphibians can because their skin, like that of a fish, is permeable so they have to keep themselves damp. Water is both inside and all around a fish so there is no need for an impermeable barrier but that means water moves across the skin layer all the time – by osmosis – and the fish’s organs have to balance that. A sudden change throws that out and the fish will be stressed until it has achieved balance again. If you need to make a change, do it slowly.
When I started keeping fish, in the 1970s, it was an accepted fact that you had to make the water you used to change your tank exactly the same temperature as that in the tank or you would kill the fish. For years I would boil kettles and mix that with the cold water in my buckets but no more. Why? Because it is nonsense! I change 25% of the water in my tanks every week and use water from the tap, through the carbon filter and into the tank. I run it in slowly so that the new water can be dispersed by the water flowing around the tank but I don’t heat it and I’ve never killed a fish. I may even have induced some to spawn as some species are triggered by the cool melt-water coming off the mountains in Spring and chilling the water that they’ve been living in by 5 °C or more. Where did that myth come from? Goodness knows but it was widely held at the time.
One final thing: tap-water varies across the country. In Derby it comes from the southern Peak District and has some hardness but not too much so I rarely have to descale anything. Twenty miles away, my father’s water comes from boreholes near Burton on Trent and has a lot of gypsum in it, which is great for brewing but leaves lots of lime behind in his kettle. Around Wigan, the water is very soft and friends can keep discus with ease but have to spend a fortune on salts for any Rift Valley cichlids they have.
So I hope I’ve made you think a little differently about water. It’s a lot more complicated for us fish-keepers than outsiders might think. The crux of the matter, though, is that you need to know not only what your fish need from their water to do well but what is in your water, too. Get the water right and your fish will thrive. Don’t bother and you’ll be simply chucking your money away, along with the fishes’ bodies.
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