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Pool Ideas For A Tropical Island


JackT

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Hey guys,

We are evaluating an idea to put an inground pool in our new B&B which will be in one of the South Pacific islands. There is access to concrete (hand mixed), concrete blocks, rebar, however no mains power (solar only). The ocean is around 130ft away.

What would be the best way to do this, probably 15,000 gal size. Been reading a lot about the chlorinated (nor practical, would need to import chlorine), saltwater (maybe could use filtered ocean water?) and ionized pools (sounds good, is it for real?). Also given that there is no cheap power there, we have to rely on solar. I saw some designs with floating solar filters, submerged filters based on marine bilge pumps. Others use a DC pump as the main pump, would that, if combined with ionizer, be enough to clean the water?

Also, the fresh water is less abundant than the seawater, that got me thinking about saltwater setup. What do you think?

And the last question, has anyone had any experience with pools in tropics - are they difficult to maintain, what are the common issues etc.

Thanks in advance to everyone who responds, I appreciate your time. Having never had a pool in my life I am not sure where to start.

Thanks,

Jack

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First, ionizers don't/won't cut it, ever.

At 130' from the beach, the water table will likely be high. This will keep at least some of the pool above the earth. That will mean thicker walls or raised earth.

I am not a fan of using filled blocks. The blocks usually aren't as strong as a poured wall and floor. The use of forms for the walls with reinforcement from a rebar mesh and a vibrated pour will provide an air space free wall structure that is strong enough. Hand mixed? That's a LOT of labor, even with cement trucks and a wheel barrow brigade. Consider a fiberglass pool if you have a way to carry it like a crane or track hoe. A liner pool with enough back fill or an above ground pool might be a better option. An above ground, with a deck around it can look just as nice.

I am assuming the US standards for the construction of a commercial pool are not needed. Are there any construction requirements the local government maintains must be met?

The use of sea water is NOT recommended. There are a lot of electrolysis related concerns and special equipment needed. Operation, spare parts, and chemistry will present a lot of problems you don't want to go through. The use of fresh water is strongly encouraged. With a properly maintained pool, you will minimize water usage. While there are sea water capable systems, they are awfully expensive.

Sea water has about 40,000 ppm of salt. A salt water chlorine generator will only need 3500 +/- 500 ppm in the water. At 3500 ppm, regular residential gear would work fine. That will minimize the need for bringing in other chlorine sources such as cal-hypo, dichlor, unscented bleach or chlorinating liquid (just a stronger bleach). The cell will handle most of your daily chlorine needs but you will still need to raise the level for chlorine periodically and balance the water with some dry goods like sodium bicarbonate (aka baking soda) and others. Have a weather proof storage room for their safe keeping. The amount of space will depend on the pool size, bather load, and length of time between resupplies.

Expect about a 3000 watt demand at 240 VAC (50/60 Hz) on the solar array/battery storage. This gives you a little head room for the pump, salt cell and lights (LEDs use 90 watts max for each fixture and usually less vs. up to 500 each for a white incandescent fixture).

Tropical storms and cyclones are the biggest issue. They can blow in debris, dilute the chems in the water, and bless you with algae. The need for on site spare parts is suggested for timely repairs. Watching your pool go green because the motor failed on the pump and waiting two weeks for a spare to be shipped (and that's a rush job too!) is also troublesome. As I said before, having a weather tight storage facility will be important.

Scott

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Thank you so much for your reply, Scott!

Ok, will answer your questions first.

There are no regulations per se, i.e. no pool fences required etc, in fact there are hardly any regulations for building, unless it is a multi-story building or similar.

The location is actually higher than sea level, I would say 40 feet higher - so the water table shouldn't be an issue at all.

Would love to use a fiberglass shell however it would have to imported and as if it wouldn't fit into a shipping container I can see some potential issues with that idea. The simplest way of building things there is concrete blocks as they are manufactured locally, anything else has to be imported.

Can you tell me the wattage of a typical salt water chlorine generator cell?

Also I have read quite a few people successfully using big marine bilge pumps for circulation (using cartridge filters, not sand filters), which makes it very economical to run electricity-wise and the pumps are available. I have also seen some DC pumps for pools, that sounds like a good idea. I have set up some solar myself and prefer to keep everything DC if possible. You will appreciate the need for the simplest setup possible - the island is known to run out of toilet paper sometimes! The simpler it is, the better. Having the pump replacement on standby is a must.

Also I can get very nice and powerful LED spotlights that only use a few watts of power - that sounds like a way to go? Do the underwater fittings accept standard LED (or halogen if it was on the grid) spotlights?

As you have noted I am too mostly worried about the weather aspect. There are heavy downpours sometimes every night so will that upset the salinity? I.e. would the salt (or chlorine) need to be added after a rain storm, every time? Or does it affect pH more than anything, due to debris etc?

Once again thank you very much for your time and I will appreciate if you can find some more to answer the above as well.

Cheers,

Jack

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A bilge pump won't do it AFAIK. Bilge pumps need a sump to sit in and are not self priming. That mean digging a pit so it can get enough water from the suction plumbing via gravity/air pressure. It would also need to move at least 40 gallons a minute for a number of hours. That is a lot of water to move and that costs wattage, at least a 1/2 HP (746 Watts = 1 HP) plus the motor's Service Factor multiplier. Getting enough water to flow into a sump without suction will mean a lot of added complexity. Figure a 1/2 HP motor with a 1.5 SF rating would draw 4-2/3 amps at 120VAC or 2-1/3 at 240VAC. It also would make manually vacuuming a pool very difficult.

Figure a salt cell is good for about 500 watts.

A pool is not built with single story structure strength in mind. The pressure of the water trying to escape in all directions except up, and any land movement is likely to cause the shell to crack unless there is a rebar mesh, encased in cement, supporting the shell. The concrete needs to be at least 3500 psi rated and at least 6" thick on the floor and thicker on the walls, especially the top foot which needs to be 12" and with extra rebar used to form the bond beam.

I don't think blocks will do it. They are great for supporting a vertical structure but the forces exerted for a pool are not just vertical. They aren't made for that.

Pool lights are flood type in nature, not spots. The fixtures are also water proof and meant to be submerged. In order to get enough lumens in the water, higher wattage fixtures are needed. It's one thing to illuminate an air space and quite another to illuminate a water space.

Scott

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Thanks again Scott,

One more question - I see ozonators advertised and it sounds like with right calculations a system could be built that uses ozonator only, i.e. no chlorine whatsoever - is that correct? Definitely guys selling them seem to think so...

Jack

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Ozone only? Hello algae. Hello person to person transmission of infections and the like. Hello to an increase in bather wastes in the pool. Ozone is not a primary sanitizer. It can only augment it. If someone is touting otherwise, either the person representing it that way has no clue how and or why it might work or the snake oil salesman can safely be given.

AFAIK, ozone has no effect on algae. It will grow.

Ozone has a short half life. It breaks down quickly. therefore, there can not be a useful residual in the pool. It won't last long enough. It takes up to five turns of the water volume to filter all the water in most pools. Since the ozone injection point is normally on the suction side of a pump, it takes an equal amount of water to pass (five turns worth) to potentially (the ozone molecules may miss the target since the concentration is low) oxidize the water. With a residual sanitizer in the pool's water, chances are that anything that needs oxidizing, such as sweat and tanning lotions, has already been gotten at before it hits the ozonated water at the pump.

Just for argument's sake, lets shut the pump off at sundown. In an hour or so, all the ozone will be gone. In a B&B with a pool, what are the chances someone will want to swim one night, before bed. Sweat, tanning lotions, dead skin, and any other form of bather waste is now in the pool. And for how long?

Let's say it rains. Rain can carry algae spores. You'd soon have an algae bloom in the pool and ozone injection couldn't do anything about it.

Scott

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Thank you once again Scott, this has been really helpful.

If building from concrete blocks I would put a lot of steel in them and fill them in with concrete as we go up. Being all manual mixing it is not possible to fill it all in one go with a pump (No pump. No concrete trucks) so the walls would be filled two or three rows at a time, adding horizontal rebars too.

Do you think it would be better to lay down the steel in the pit and walls and then keep pouring concrete on it - however it would have to be pretty thick to keep the shape until it sets. Blocks would act as forms, albeit at an additional cost. I wouldn't think of building a pool out of blocks only, as you said it wouldn't be very strong and also there are earthquakes there too...

Cheers and have a good day,

Jack

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I really think you'll be better served bringing in a vinyl liner kit.

I have little confidence in a filled block wall. You'd need #4 rebar, 12" on center or better and the side walls of the block to be able to support the pressure without crumbing the cement holding their aggregate. The block used in construction here in the North East are called cinder blocks and contain a lot of aggregate. If you have the same type, they are great when pressing weight from above but, even when filled, the actual block may deteriorate because of the pressure.

A denser cement block with more cement and a finer aggregate will be needed and a 10-12" bond beam around the perimeter built. The floor almost has to be poured. A 6" thick floor with #3 rebar on 12" centers is the bottom line with 4000 psi concrete. Those rebars need to climb up the wall and block be inserted when building the wall. Seems the idea of laying horizontal rebar more than every row would exceed the minimum strength I see needed. Dobies will be needed to keep the rebar in the concrete.

Any in-ground kit will need excavation. With a liner kit, you can over dig the hole some for walking room. to put in plumbing.

I'd use either a sand bottom or 2" cement with chicken wire mesh reinforcement, assuming a sandy bottom. Somehow, I can't see a clay bed being there.

Back filling is easy with sand plentiful. It'll come on pallets and boxes. Just know what depths you want so the liner gets made right.

It's just so much faster and easier to put a liner pool in your location.

Scott

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