Do You Have To Use Reverse Osmosis Water?

Reverse osmosis (R/O) water seems to pop up very regularly in questions and discussions. Some aquarists consider the R/O filter to be another piece of equipment that is not really necessary. There is quite a bit of confusion particularly with beginners, which is understandable when the whole spectrum of equipment and guidelines for keeping marine systems is considered.

The heading question can be answered straightaway – no, you don’t. If you’re lucky, and have a water source such as a well that provides water of high purity, or live in an area where tap water is of a really high standard and not polluted with nitrates, insecticides, metals, bacteria (I won’t go on) then the tank seawater mix could well be of high quality.

Some aquarists have tried using bottled spring water and found that the purity was in fact not as thought and/or the cost was prohibitive. Similarly, some have obtained a supply of distilled water from a chemist or other source and tried that. This proved to be an inefficient way of obtaining the amounts of seawater – multiple gallons – often required, plus the cost.

A few other aquarists have turned to Mother Nature, a fine choice provided the transportation and storage needs can be met, and an unpolluted source can be found.

So for the majority it is the household tap. The water from the mains tap is purified and regulations exist for the amounts of pollutants that are acceptable. Nitrate can be present in a surprisingly high amount, as can phosphate, plus the insecticides etc mentioned earlier.

The water from the tap at the very least should be tested for nitrates and phosphates before consideration is given to using it for a salt mix. If tests are not done then the aquarist is possibly preparing a potential home for nuisance algae, particularly if high power lighting is being used. Added to the pollutants in the tap water are the natural developments in the tank because of the natural processes of the livestock, and the results of potential overfeeding.

Personally, I find it difficult to follow the logic (should I say illogic) of not using R/O water. First, look at the expense the aquarist has accepted in preparing the aquarium system, having purchased lights, salt mix, test kits, a protein skimmer, canister filter, heater(s), circulation pumps, maybe a calcium reactor etc, and also of course the aquarium and stand. Then there is the internal decoration, such as live rock and maybe sand. The fish and corals haven’t been mentioned yet! Whether a fish only or reef system, it all represents a fair sized investment.

Over and over emphasis is placed on the need for high quality water. To this end, the dry salt mix that most aquarists use is manufactured to a high purity, lacking in such unwanted substances as nitrate and phosphate. Why add less than ideal water to it?

If there is a marine retailer close by, R/O water may be available to purchase by the gallon. Quite reasonably, the retailer has to make a profit. Moving the water in containers is not the easiest practice.

If the aquarist purchased an R/O filter then production of purified water would be straightforward and predictable demand easily met. The cost of the filter, particularly when the cost of other items of equipment is considered, is reasonable.

R/O water is generally 95 to 98% pure and the environment for the aquarium livestock would be enhanced, which is probably the most important point, and the possible appearance of undesirable headache algae would be reduced.

  1. So what about the cheaper route glacier water ( These are found at many retailers and claim that they not only use R\O, but also a number of additional filters ( at 25 – 30 cents a gallon it is cheaper that a aquatic store, and many location are available 24 hours for those “oops” nights. Anyone have any thoughts? has any testing ben done on the true quality of this source (results would vary as it does use local water system to for it’s source)?

  2. Hi.
    I’ve not come across “Glacierwater” before, so had a look at the website you provided.
    I too would be interested to know if anyone has tried this.

  3. I use Glacier and I like it so far. They said that there are no prosphates or silicons in their water

  4. hello :
    i have a 250 gallon aquarium , good bio home made filter ,ehiem mechanical filter for 1500 l , a protein skimmer ,uv lamp , good lighting .
    i want to setup a reef aquarium .
    my question is :
    do i need an Ro system for my tap water ( there is no nitrite in my tap water ) or can i just use the( water conditioner )

  5. Hello.

    There may be nitrate in your tap water or quite a number of other things caused by industry and/or agriculture. The water authorities put chlorine or chloramine in the water too as a cleaning agent. We don’t require any of it!

    I would suggest that an RO filter would be worthwhile. You will know that you are mixing the purest water you can.

    RO filters are not very expensive and are easily maintained – in fact they require little maintenance. It is best to check the amount you will need for routine seawater changes and size the RO filter to that. The filters come in various ‘gallons per day’ sizes.

    It is also good to initially fill your aquarium with RO water, not tap water. This takes some time, but is worth it as from day one the seawater is as good as it can be.

    I’m not sure what you mean by ‘water conditioner’ but assume it is a household conditioner. Many of these are based on carbon and are nowhere near as good as an RO filter – so as said I suggest the use of the RO filter.

    Johns last blog post..Should You Use An Automatic Fish Feeder

  6. your posting about RO Filter is very beneficial for me, keep it up.Thanks for Sharing information.

  7. Glad the text was OK. Your equipment is a bit big for most home aquariums!

  8. That’s what I was seeking for, what a stuff! existing here at this blog, thanks.

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