Taking the mayhem out of marine fish keeping
Water almost seems so obvious you may rightly wonder why on earth there is a full page dedicated to it. There are, however, many different kinds of water. Tap water is usually perfectly adequate for many tropical fish tanks and time and again I get asked 'well why can't i use it for marine?' Rainwater is easily accessible in this Country and again I get asked 'why can't I use it, I have water butts full in the garden'.
The simple answer is no, don't use rain water, don't use tap water, use water that you know will do the job. Marine salt water is complicated enough without added issues brought on by using water that you don't fully know the chemical composition of.
Think of it another way, if you get any problems down the line with algae, sudden fish deaths, can't balance parameters properly (and chances are one of these will apply to you at some time or another), the first thing to look at is the water quality. There are lots of chemicals we can't, as a hobbyist, test for so a nasty something or other could be present in your water for months without you ever getting to the bottom of the cause of one or more of your problems. If you know exactly what's in your water you are halfway to solving your problem.
The Marine Tank Environment
There really are so many potential undesirables in your tap water that I strongly recommend not using it, from traces of the female contraceptive pill to chemicals like liquified chlorine. In addition, as I've already mentioned two of your biggest enemies when running a budget marine tank will be nitrate and phosphate. These are often present in high amounts in tap water (phosphate, for example can be present in up to 150 times the desired amount in a marine tank) so you would be fighting a loosing battle trying to control these in a marine environment if you're using tap water.
The most popular water used in the marine hobby is referred to as RO or Reverse Osmosis water. The detail of how this is produced us currently beyond the scope of this website (I will add another page at a later date just on this process), for our purposes we'll just think of it as a highly filtered type of water, so filtered its almost back to its pure H2O composition.
RO water is commonly for sale at most marine fish shops either salted or unsalted. One warning I would give, however is that you have to consider that fish shops are churning out gallons of this stuff per day and the quality isn't necessarily absolutely perfect. I (and many others) would therefore recommend you investing in RO unit yourself. You will save financiallly in the long run if you produce your own RO water and many are now availible for £100 or less. It doesn't take a genius to work out how to plumb one in and once its there you can usually tuck it away in a cupboard under the sink so it can be discrete.
Once you have your pure base to start from (pure water) you will add marine grade salt to it. Again the benefits of starting with almost pure water will become apparent as the different chemicals in each salt are measured so you have a good starting idea of the levels of your parameters. This will become even more important at a later stage should you decide to progress to the more demanding corals such as sps.
So it's all about the water
Always think of the health of your tank in terms of its water
Never get complacent about water changes, regardless of what you end up keeping water changes are an excelllent way of maintaining many of the parameters required to keep a health tank.
Water - in a nutshell
You always need to consider that one of the most important things in marine fish keeping is keeping the water in tip top condition
Never be tempted to use tap or rain water in your marine tank, even if everything seems great at the beginning you will run into problems further down the line
The biggest problem you will have for the life of your budget tank will be phosphate, tap water can hold up to 150 times the desired amount of phosphate that you would want to see in a marine tank
Reverse Osmosis is a way of making sure your water is as pure as you can get it
Start off with pure water, think of it like a blank canvas, you know everything that you have put on it (or in it) therefore if you get any problems down the line you know exactly where your starting from
Don't scrimp on the brand of marine grade salt you use, if you start this hobby off with good quality water and good quality salt half of your potential future problems are solved