Ok - so here it is:
Buyer's guide to marine salt
Matt Clarke looks at some of the many commercial salt mixes on the market and checks out their composition in this special buyer's guide.
Copyright © Practical Fishkeeping
Commercial salt mixes make water similar in composition to natural seawater. They?re usually designed to make water of the correct chemistry when mixed with hard, alkaline tapwater. When using demineralised water such as that from a reverse osmosis unit or de-ioniser, certain important elements may be lacking when the salt is mixed.
Unfortunately, high levels of nutrients in UK tapwater make it important to use purified and demineralised water for marine aquaria. If you keep inverts, you may need to add calcium, magnesium and other chemicals to bring the water in line with the composition of natural seawater.
Salts differ not only in what major and trace elements they contain and in what concentrations, but also in the nutrients and impurities.
Research suggests many salt brands do, at times, contain phosphate, nitrate, silicate, and even ammonia and nitrite - although these are often present at very low levels.
Some manufacturers say the presence of such nutrients is due to interference by certain constituents in newly mixed saltwater that lead to false positive results, or pollutants already in the source water.
While this may be the case, tests on prepared seawater using much more sophisticated laboratory equipment reveal similar results.
Research suggests ammonia is sometimes found in freshly prepared seawater. It?s thought to enter the salt as a contaminant in magnesium and calcium chloride. This stresses the importance of testing prepared saltwater before use and of proper mixing, preferably over at least a couple of days.
Some salt mixes are produced using larger quantities of hydrated chemicals than others, so they feel slightly damp to the touch. While this may keep costs down a little, it means they sometimes mix to a high pH (over 9) and may not mix to the correct salinity as some of the salt?s weight is made up by water.
Keep salt in a dry place, preferably in an airtight container.
Cost
Your annual salt bill depends on the salinity of your water, the size of your tank and frequency of water changes. According to our recent reader survey, most of you are running tanks of about 200 l. (44 gal.). Recommendations on water changes vary, but I?ve usually found 25% fortnightly is fine for the average reef tank. This means you?ll need enough salt for about 100 l. of water a month, or a little over 1,200 l. per year. That?s about 42kg, or ?100, a year - depending on how you look at it. Buying in bulk where possible works out cheaper.
The tests
Saltwater is complex and we don?t have the facilities (or the chemistry qualifications) to test it with the extreme accuracy required. Sadly, most aquarium test kits are not that accurate.
But we?ve done some basic tests and backed them up by examining results of independent research by Dr Craig Bingman and Dr Marlin Atkinson of the Hawaii Institute of Marine Biology, published in the Journal of Aquariculture and Aquatic Sciences in 1999. Their research compared the chemical
characteristics of a range of aquarium salt mixes to a control sample of natural seawater.
We?ve also sought opinions of readers, and professional hobbyists in the trade.
It?s worth adding that the Hawaiian research paper we?ve used is a little old now and the formulations of some of the salts here may have changed slightly since then. While largely well received and respected by professional aquarists and those whose salts appeared favourably in the analyses, the results have been strongly opposed by other manufacturers.
In our tests, we used purified and demineralised water from a reverse osmosis (RO) unit, so the calcium levels and pH levels we recorded could go a bit higher if you?ve got hard, alkaline water with a high pH. Tests were undertaken using Merck, Tropic Marin and Salifert test kits.
What?s in salt water?
Seawater contains all known elements, so it?s much more than just sodium chloride and water. Some of these elements like calcium, magnesium, chlorine, strontium, potassium, boron, fluorine and sulphur are present in fairly high concentrations, but others - the trace elements - are found in much lower levels.
What?s on the market?
Everyone has different ideas on which salt is best, so you?ll hear conflicting opinions. Most people try a few different ones before settling on one they like.
The results depend on the quality of water you prepare the salt mix with; what works for you might not hold for someone using different water, or who keeps different organisms.
Almost without exception, all of the salts available in the UK are of superb quality; you should get good results from any of them.
Reef Crystals
Reef Crystals from Aquarium Systems contains additional calcium and other elements. This aims to boost levels over that of natural seawater, making it well suited to the reefkeeper who uses RO. It contains a metal detoxifier to neutralise copper that may be present in domestic water supplies, and has added vitamins. It?s claimed to be the fastest dissolving salt, and has a unique crystal structure.
Hawaii Marine Institute?s research: Their research suggested that like the salts on review here, Reef Crystals didn?t produce water of the correct salinity if measured out by weight, being some 6g per litre lower than it should have been.
It came out average in most areas with sodium, magnesium, calcium, calcium carbonate, potassium, strontium, chlorine and sulphur levels all very slightly lower than the levels measured in natural seawater. Only boron was present in greater quantities.
Nutrients were present in greater quantities than in natural seawater, with phosphate levels over 25 times higher, and ammonia levels 39 times higher. The pH of the prepared saltwater was found to be 9.28, the highest measured.
Our tests: We found that the specific gravity was about 1.024 at 25?C and measured the pH at around 8.6. Calcium and magnesium levels were the highest in the test at 446ppm and 1410 ppm respectively.
No ammonia, nitrite or phosphate were detected, but we did find 0.2 ppm of nitrate, a minuscule amount really - and most of the other salts tested positive for this too.
True to its claims, the salt dissolved very quickly, taking just 90 seconds of stirring to dissolve 35g in one litre of water. At the end, however, a few larger particles appeared to have precipitated and were still present in the water.
You say: Reader Simon Orr of Devon was recommended Reef Crystals by a friend and uses it in his reef tank to change about 10% of the water weekly. He rates it very highly for dissolvability, as does reefkeeper Paul Spencer of Hull who appreciates its value for money.
John Dalley from Leeds recently changed over to Reef Crystals. ?I noticed that with my old salt, when making up water for water changes, which I do in 50 l. black plastic mausers, a white film would appear on the bottom and sides of the mauser. If left uncleaned, this would build up and flake off causing the water to go cloudy. I presumed this was undissolved salts. I get it to a far lesser degree with Reef crystals.?
Size/cost: 2kg/60 l. ?9.99, 4kg/120 l. ?17.75, 8kg/240 l. ?32.95, 20kg/600 l. ?79.99, and 30kg/900 l. ?113.97. This equates to 12.5p-16.5p per l.
Verdict
> What?s Hot
High in calcium and magnesium
A great, economical salt for RO users
> What?s Not
Alkalinity a little low
Price 8/10
Value for money 8/10
Composition 8/10
Nutrient content 8/10
Dissolvability 7/10
Overall 8/10
Instant Ocean
Instant Ocean from Aquarium Systems is a well-established brand with a fairly large following in the USA.
Hawaii Marine Institute?s research: Their research found it to have the lowest levels of inorganic phosphate of any of the salts tested, with just a quarter of the amount found in natural seawater. Nitrate levels were also among the lowest tested, at just five times the amount seen in natural seawater. However, ammonia levels were high (second only to Kent Marine), at about 51 times higher than seawater.
Sodium, magnesium, calcium, calcium carbonate, potassium, chlorine and sodium levels were all slightly lower than natural seawater, but were a little higher than the concentrations measured in the Tropic Marin. Strontium and boron levels were a little higher.
The composition was broadly similar to that of Reef Crystals, with the only marked differences being a little more strontium and ammonia in the Instant Ocean, and a little more phosphate and nitrate in the Reef Crystals. It mixed to a good pH at around 8.35.
Our tests: Like the Reef Crystals from the same company, we found a few large un-dissolved particles were present after dissolving the majority of the salt, although it did dissolve very quickly. Again, we couldn?t detect any nutrients (other than 0.2 ppm of nitrate), and again the specific gravity was 1.024 at 25?C. The calcium level was measured at 412ppm and the magnesium as 1230ppm.
At 8.6 the pH was a little high, but the alkalinity was the highest recorded.
You say: Reader Martin Ward of Northamptonshire was recommended Instant Ocean by a friend and changes about 20-30% of his water every week. He rates the salt highly, giving it almost top marks for dissolvability.
One leading retailer suggested that it seems to cause a slight blue haze when viewing through very large tanks.
Size/cost: 2kg/60 l. ?8.75, 4kg/120 l. ?15.40, 8kg/240 l. ?28.75, 20kg/600 l. ?65.99, and 30kg/900 l. ?94.03. Exceptionally good value at between 10.5p-14.5p per litre. A great all-round salt.
Verdict
> What?s Hot
Well respected. Lowest phosphate and nitrate levels measured in independent analyses.
> What?s Not
pH a little high
Price 9/10
Value for money 9/10
Composition 8/10
Nutrient content 7/10
Dissolvability 7/10
Overall 8/10
Tropic Marin
Tropic Marin salt, distributed by Tropical Marine Centre (TMC), is one of the most popular and widely used salts in the UK with a reputation for producing good quality water at a consistently high standard between different batches.
It?s made from the highest grade pharmaceutical grade ingredients which include over 70 trace elements. Interestingly, these are added to the salt as ?solid solutions?, which means that unlike other salts, they shouldn?t precipitate when the salt is dissolved. It?s guaranteed to be free of nitrate and phosphate.
Hawaii Marine Institute?s research: Tropic Marin came out top for producing water with the salinity closest to natural seawater, suggesting that it contains less hydrated chemicals than other marine salts and making it one of the best salts to purchase weight for weight.
The independent research showed sodium, magnesium, calcium, calcium carbonate, chlorine, boron and potassium levels were all close to the levels found in seawater. However, organic phosphate concentrations were the highest at around six times that seen in natural seawater at the time of the tests, but by contrast, silicate levels were among the lowest. Nitrate levels, although some 11 times higher than those seen in natural seawater, are about average among the salts on review here. And at just two to three times higher, ammonia levels were one of the lowest recorded. At 8.9, it was found to mix to a rather high pH.
Our tests: Our tests however detected no phosphate, ammonia or nitrite, but we did find a trace of nitrate at 0.2ppm.
The salt mixed to a pH of 9.0 in our tests, which is rather high. Calcium and magnesium were both rather low, as were the KH and alkalinity. The salt dissolved quickly, with no precipitation and no residue.
You say: Our reader survey suggests that Tropic Marin is the most widely used salt, and that you?re all happy with it. Most of you were recommended it by friends and shop staff, and you rate it highly for dissolvability.
Tropic Marin is also quite widely used and well respected in the aquatic trade. When asked why he used Tropic Marin over other salts, Jason Scott, of the WaterZoo in Peterborough, said: "First, TMC keep all their livestock in it, so there?s less of a transition for them to make when they?re acclimatised to our tanks. Second, we make regular visits to TMC so we can collect it when we?re there, and third, other brands seemed to cause us to have a very high calcium level (500ppm+)".
Size/cost: 1kg/30 l. ?8.99, 4kg/120 l. ?15.60, 10kg/300 l. ?34.28, 20kg/600 l. ?70.62, 25 kg/750 l. bucket ?89.87.
At 12p-30p per litre, Tropic Marin is the most expensive salt here. You can make considerable savings by buying in bulk.
Verdict
> What?s Hot
Good reputation for reliability
> What?s Not
Mixed to a high pH
Requires additional boosting if used with RO
Price 5/10
Value for money 6/10
Composition 6/10
Nutrient content 8/10
Dissolvability 7/10
Overall 7/10
Kent Marine
Kent Marine salt is often available at very competitive prices, and has a pretty good reputation for quality and reliability, so it?s little wonder that it?s becoming more popular in the UK. It contains additional calcium, strontium, iodine and trace elements, which means that it?s one of the best salts to use if you use demineralised water, like RO.
Hawaii Marine Institute?s research: Kent Marine salt came out well with magnesium, calcium, calcium carbonate, strontium and boron all present at levels slightly above those found in natural seawater. Similarly, calcium and buffering levels were the highest seen in any salt. Sodium, potassium and chlorine levels were all slightly lower than in natural seawater.
In these independent tests nitrate levels were found to be 10 times higher than the level found in natural seawater, which is about the norm, and ammonia levels were nearly 60 times higher, which is rather high.
It may contain more hydrated chemicals than some of the other salts here, because 35g produced a salinity of around 28.85ppt ? one of the lowest found, which means that by weight it doesn?t go as far as some other salts on review here. It mixed to a pH of 8.08 ? the lowest recorded in the independent analyses.
Our tests: Our results were broadly similar, but showed no phosphate, ammonia or nitrite, and just 0.2ppm of nitrate. It mixed to a pH of 8.4 and dissolved quickly leaving no residue.
At over 440ppm, the calcium level measured was one of the highest recorded and is a good level for coral growth. Magnesium levels were also very high, although the alkalinity was a little low.
You say: Ian Abraham of Berkshire chose Kent because of its price. He changes about 10% of his water every week. He gave it nearly top marks for dissolvability and doesn?t add trace elements.
Kent Marine is another very popular salt according to our survey. You rated it very highly for price and dissolvability, and again you all seem very happy with it.
It?s an impressive all-round salt, well suited to the modern reefkeeper and excellent value for money.
Size/cost: 25 US gal. (94 l.) ?13.99, 50 US gal. (189 l.) ?23.99 and 200 US gal. (757 l.) bucket ?86.99. Price per litre varies between 11.5p-15p.
Verdict
> What?s Hot
High in calcium and magnesium
Informative packaging
Enriched formula ideal for use with RO
> What?s Not
Alkalinity a little low
Price 9/10
Value for money 8/10
Composition 8/10
Nutrient content 8/10
Dissolvability 7/10
Overall 8/10
Seachem Reefsalt
Hawaii Marine Institute?s research: Seachem scored quite well for calcium in the Hawaii Marine Institute tests. The calcium carbonate, magnesium and chlorine levels were the lowest recorded, and the buffering capacity was also rather low compared to the other salts in Hawaii?s analyses.
At over 90 times greater than the concentration found in natural seawater, nitrate levels were by far the highest recorded in the independent tests.
However, ammonia levels were among the lowest. At 8.81, the pH was rather high. On the plus side, sodium, potassium, strontium, sulphur and boron all scored particularly well ? almost matching the levels seen in natural seawater.
Our tests: Our rather more basic tests revealed a pH of 9.0, a calcium level of 362ppm, the lowest recorded, and a magnesium level of 960ppm, which is slightly below average. The alkalinity however, was pretty much spot on.
We found Reefsalt a little slow to dissolve and there was some residue left in the vessel after mixing.
Seachem reef salt comes in a special heavy duty, hermetically resealable bucket. A great idea for keeping the salt fresh. The only drawback is that it takes a bit of wrestling, some brute force and a sturdy screwdriver to get the lid off.
Size/cost: Seachem salt is available in the following sizes: 100 l. ?19.95, 200 l. ?29.80 bucket, 600 l. ?79.95 bucket and 3,800 l. box ?399.95. Price per litre varies between 9.5p-20p per litre.
Verdict
> What?s Hot
Ideal alkalinity. Resealable bucket
> What?s Not
Low in calcium and magnesium
Mixes to a high pH
Slow to dissolve and leaves some residue
Price 6/10
Value for money 5/10
Composition 6/10
Nutrient content 6/10
Dissolvability 6/10
Overall 6/10
Red Sea Salt
oral Reef Red Sea Salt is made largely from natural salt, rather than from laboratory mixtures of the constituent chemicals. Red Sea claim that in their tests, this results in a significant difference in coral growth over pharmaceutical grade salts.
Contrary to popular belief, it?s not a by-product of desalination plants. It is produced in Israel especially for the aquarium trade. It has some trace elements added to enable it to produce water of the correct composition.
Hawaii Marine Institute?s research: In the independent tests, Red Sea salt came second only to Tropic Marin for producing water of the desired salinity, but it was still around 5ppt (grams per litre) lower than it should?ve been at a little under 30ppt.
Sodium, magnesium, strontium and boron levels exceeded that found in natural seawater, and all other levels were fairly close to those seen in nature. Calcium carbonate levels, however, were the second lowest recorded.
Nutrient wise, Red Sea salt was found to be particularly good, scoring very well for phosphate, nitrate and ammonia. It mixed to a pH of 8.69.
Our tests: Our tests saw the Red Sea salt mix to a pH of 8.4 (which along with Kent Marine was the best we recorded), and we found just 0.2ppm of nitrate. The magnesium and calcium levels were both very good, and the alkalinity was well above average ? but a little higher than you?d see on a natural reef.
Size/costs: 1kg/30 l. ?4.90, 2kg/60 l. ?8.95, 4kg/120 l. ?16.50, 6.33kg/190 l. ?22.95, 20kg/600 l. ?67.95, 25kg/750 l. ?84.95 (bucket), and 40kg/1200 l. ?129.95. Price ranges from 11p-16.5p per litre.
Verdict
> What?s Hot
Very low in nutrients
> What?s Not
Low in calcium carbonate according to independent research
Price 8/10
Value for money 8/10
Composition 8/10
Nutrient content 7/10
Dissolvability 7/10
Overall 8/10
Waterlife Ultramarine
This was one of the first commercial salt mixes and was developed in the UK in the 1960s.
Like most other salts here, it?s made from high grade pharmaceutical ingredients and contains no added nitrates or phosphates. Unlike most other salts, it contains additional additives including vitamins and even dechlorinator. This British salt wasn?t tested in the Hawaii tests, so there?s no scientific data to compare to our results.
Our tests: Ultramarine salt proved to be by far the slowest salt to dissolve and left a lot of hard, gritty residue in the mixing vessel as well what appeared to be some precipitation on the sides. At 8.6, the pH was about average. The calcium level (366ppm) and the magnesium level (990ppm) were both a little below average. The alkalinity was the lowest we recorded.
We found no ammonia or nitrite, but did detect 1.0ppm of nitrate and 0.015ppm of phosphate, both of which were the highest we recorded. Not terrible, but not quite up to the excellent
standard seen in the other salts we tested.
Size/cost: 25 l. ?4.90, 50 l. ?5.63, 100 l. ?10.35, 250 l. ?25.54, 500 l. ?45.50, and 1350 l. ?120.59. Even the smaller
sizes come in handy resealable containers. Prices range from 9p-20p per litre.
Verdict
> What?s Hot
Resealable containers
> What?s Not
Highest nitrate and phosphate levels we recorded. Lowest alkalinity recorded
Price 6/10
Value for money 5/10
Composition 5/10
Nutrient content 5/10
Dissolvability 4/10
Overall 5/10
Literature cited
For further information on the Hawaiian Marine Institute?s research, see Atkinson, A. and Bingman, C. (1999) - The composition of several synthetic seawater mixes. Journal of Aquariculture and Aquatic Science, 8 (2): 39-43.
