The marine aquarium, be it fish only or reef, needs quality seawater for health. Quality seawater is the number one on the list of requirements for success. This is more easily achieved nowadays.
First of all, the aquarist will usually obtain sea salt, online or from the local dealer. This sea salt is of high quality and is fairly expensive probably best bought in reasonable bulk. It has all the constituents required mixed in at the correct levels. Some aquarists use natural seawater and there’s nothing wrong with this provided there is absolute surety that the seawater is not contaminated. Let’s go with the purchase of sea salt.
As said, the sea salt includes all the necessary constituents to make high grade seawater, but there is one possible failure, mixing with tapwater.
We drink tapwater so what can be wrong with that? Well, depending on the area, the water authority could well have put additives in to ensure the safety of humans, additives such as chlorine. Also pesticides, phosphates, nitrate etc could be present particularly in farming areas. These are definitely not wanted. We want, as far as possible, good uncontaminated seawater. If the fresh water has been tested and is definitely clear of contaminants then fine.
So what can be done to avoid allowing contaminants into the aquarium? Nowadays it’s very easy and straightforward. Go online or perhaps better visit the local pet store and check the RO Units available (RO means reverse osmosis). There are a lot available. These units usually produce 95 to 98% pure water, removing contaminants. They’re just the job for the aquarist. They are usually driven by tap-water pressure and have two dripping outputs, one is faster for waste, the other is the water for use in seawater mixing. A non-contaminating container for the required water is needed and, if wasting the rejected water is not wanted then this can also be collected and used for example on the garden. Maintenance is required, for example RO units usually run the tapwater through activated carbon and this requires changing at wide-ish intervals. There are clear instructions with the RO units.
The water going through the RO unit goes through activated carbon (and other filtration agents in some RO units) and then through a micro filter. The activated carbon is necessary to protect the micro filter from chlorine as well as collect other contaminants. This is how the high purity of the water is achieved. Generally speaking, for every 5 gallons of water which goes through an RO unit, about 4 gallons will go to waste. Waste is reduced if the calcium content of the water is lower. If intending to collect both outputs from the RO unit these amounts should be born in mind.
Choosing the correct RO unit is important. RO units could have differing output speeds. The aquarist will be aware of the gallonage, preferably the net gallonage of his/her aquarium. A dripping output can produce a lot of water but it takes time. Knowing the amount of water required for a partial change the time producing it can be worked out ensuring that a suitable RO unit is purchased. If required the RO unit can be fixed permanently where the collection container(s) can be stored.
What about some more tests? Oh, no! Simple and not very often, the output from the purified drip of the RO unit needs to be checked for nitrate and phosphate. It will probably be fine, but a check if only for reassurance is needed. Best to be sure high quality water is being produced.
The new aquarist with a new aquarium is usually in a ‘go, go, go’ mood. Filling the aquarium with sea salt mixed with RO water is patience testing. Many gallons are required, much more than for general maintenance water changes, and it takes time with the ‘drip, drip, drip’ output. However, hopefully it’s a once only effort (exercising that so important patience) and future partial changes are not a problem. Also it should be remembered that the water in seawater evaporates slowly, but not the salt. Don’t top up with tap water, use RO water. Keep a reasonable amount, maybe a gallon or two for this purpose. Once the amount of a partial seawater change is known, then an amount can be produced by setting the system off in time.
An RO unit could be looked at as yet another outlay of money when quite a lot has already been spent. However, it adds to the probability that the aquarium will be successful which means that the overall financial expenditure was worthwhile and, very important, the aquarist is happy.