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It was December 1996 . . . about home made sea water

PostPosted: Fri Oct 24, 2008 2:51 am
by Dutchman
It was December 1996. The height of the Southern Hemisphere’s Summer holidays and the place was Port Elizabeth, South Africa. North of the city, the Swartkop river flows into Algoa Bay and north and south of the mouth there are beaches as far as you can see. The water is 25°C and the surf is mild in the protected bay. Normally this is paradise, but this day something is wrong. The sewer of Motherwell – a township north of the river – is blocked and the raw sewerage overflows into the Swartkop river and down into the bay. Luckily the current in the bay flows in a clockwise eddy moving the debris north away from the city, and people are warned to stay south of the mouth.
This is not the first time this has happened. A lot of people in Motherwell use their toilets as trash dumps and the sewer blocks frequently, but it is usually quickly fixed. This time however the blockage is solid and a section of the sewer needs to be dug up. That’s going to take some time during the holidays.
My daughter Karin and I needed sea water for our fish tanks. That’s an enterprise we normally undertook once a month, and we usually invited the entire family to join us for a beach lunch. It helped carrying twelve 25 liter bins back from the sea to the truck. As a reward, Karin and I paid for food and drinks. It used to be great fun.
But now we were in a quandary about the quality of the water. It hadn’t been that good lately, and finding spots where the water is clear and free of contaminants was becoming more and more difficult. Another point of concern was that the rocks on the seafront were becoming barer all the time. These rocks used to team with oysters, mussels, red bait and all sorts of other life. Lately it was rare to find the common barnacle. Could the bay water be that poluted?
Checking out the Swartkop mouth we could see the sludge enter the surf turning the breakers into fecal processors. No way could we use this water! Pity about the beach lunch.
On the way back we discussed ways of overcoming the problem. We could use artificial salt, but Karin told me that it took 500 Rand - about $150 at the time - just to fill up her 200 liter tank. Not a viable option. Of course, we could always make our own water from base chemicals. Karin is a registered pharmacist and I am a chemist. Surely we should be able to do this!
A week passed before Karin could track down suppliers of base chemicals selling small quantities at reasonable prices, while I was hunting down a workable recipe and equipment to do the mixing. It took another week before we arrived at a working concept. There were two remaining problems: Magnesium chloride was expensive and unobtainable in small quantities, and what to do about the micro elements which were so difficult to get. Remember, this is Port Elizabeth. There isn’t much civilization south of us, except for perhaps Antarctica, so people are excused for thinking that this is the end of the world.
To overcome the problem of the micro elements we decided to dissolve sea shells in hydrochloric acid, locally know as "pool acid", which was cheap and plentiful. We would also use raw sea salt from a nearby salt pan. This way we hoped to capture plenty of associated trace elements. Of course we had little knowledge of exactly "what" we captured.
The magnesium chloride would have to be made from the same sea shell calcium chloride by adding inexpensive magnesium sulfate, also known as Epsom salt, which would cause the calcium to precipitate in the form of gypsum.
If you are familiar with the chemistry and know what you’re doing, then these procedures are relatively simple to carry out, although it is not something one would recommend to carry out in the kitchen. However, today - 2008 - this wont be necessary anymore. Calcium and magnesium chloride is readily available in 25 liter bins of 30% concentration, and trace elements for sea water tanks can be found in many pet shops.
Finally the day to make our first batch of home made seawater had arrived. High time, because it was now one month after the last water change was due. As a safeguard we had kept our feeding regime on a very low level to reduce waste production.
We had a 55 gallon plastic bin and decided to make 200 liters of sea water. We filled the bin up with about 150 liters of plain tap water. We did not treat or test the tap water, although later on we quick-checked for ammonia. We had requested a chemical analysis from our municipality and found that it was essentially rain water with some calcium and magnesium, but no ammonia, phosphates, nitrites and nitrates, although it was treated with chloramines.
So, then we added in the same order and stirring every time after adding:
NaHCO3 (Baking Soda) 29.2 gr
NaCl (saturated raw salt 17.2 liters) 5461 gr
CaCl2 226 gr
MgCl2 468 gr
KCl 139 gr
KBr 12.5 gr
H3BO3 5.1 gr
SrCl2 2.9 gr
Mix untill dissolved. Then add . . . (pre-dissolved in ± 10 liter)
MgSO4.7H2O (Epsom Salt) 1389 gr

To measure these quantities you need two scales: One mini scale 0.0 – 99.9gr, and one digital kitchen scale 0 – 999gr.
The sea salt is kept as a saturated solution of 27.3% concentration, and is best measured in liters using a calibrated bucket.

Next, the bin was filled to about 10 liters short of the mark, and then a home made canister filter with activated charcoal plus an aerator attached to the pump was lowered in the bin to run overnight. That filter would keep the water aerated and circulating as well as removing the chloramines, organic chemicals and heavy metals such as copper.
The following morning we did our first measurements. I clearly remember the values: pH 7.8, density 1.027, requiring 6.6 liters of tap water to bring it to the target of 1.026.
I did not have a KH tester at the time, but based on the pH value I added a teaspoon of baking soda. Within half an hour the pH had risen to 8.0, but we left the bin to circulate and aerate further until the following day.
I remember that the pH had dropped somewhat the following morning and I added two more teaspoons of baking soda. This brought the pH up to 8.3, and this time I left the bin to filter, circulate and aerate for the rest of the week.
On Sunday morning early, Karin arrived to get her two 25 liter bins of sea water. I told her that I would do my water change first to see what happened. So that morning I slowly exchanged 25 liters of my 100 liter tank, and then we both watched . . .
Nothing significant happened. Nothing that we hadn’t seen before. No behavior that seemed odd, although I sat there the whole day watching them. Karin phoned later that her water change had the same effect. No problems.
The way we did these water changes - at least most of the time - was that we normally changed every weekend, but we checked our water first as early as Friday, mainly density and pH, and sometimes calcium, in which case this could require of a bit of "Kalkwasser". On Saturday we checked density and pH once again to ensure that the water would be as close as possible to the "new" water. Then on Sunday morning we did the water change.

By now 75 liters had been used from the bin, so I added about 50 liters of tap water and the appropriate amount of chemicals for 75 liters. Next day I checked the density and the pH, corrected them and left the bin for the rest of the week to circulate, etc.. and that Sunday morning we did the next water change.

We did this for the next three years, until in January 2000 Karin got married and she gave away her fish tank. I stopped mine a little bit later, and I haven’t had a tank, sea- or fresh water since. But if I ever start a new sea water tank, this is the only way in which I will get my sea water. It is convenient, cheap and not difficult at all, and it certainly beats collecting it from the sea.
Of course I wouldn’t need to make my own calcium and magnesium chloride anymore - it’s fairly easy to get these days – as are the trace elements. I would also still use plain tap water despite all the well meant advice against it. Free of contaminants - there’s nothing wrong with it. Besides, the stuff gets delivered to your house in thousands of gallons for next to nothing.
All in all, I don’t think I would change much. Even in those days, I had this method so waxed that I could make a 100 liter make up in just a few minutes. I could live with this quite easily.

Cor de Wit (aka "Dutchman")
Mad Scientist Moderator