Marine Temperature Control :


This topic covers various ways of keeping the temperature in marine tanks lower than normal.

Generally, for FO (fish-only) or FOWLR (fish-only with live rock), it is not really necessary to cool the water.
Having said that, fish will generally also do better with slightly cooler water.
At higher temp., their metabolic rates are higher, they eat and pass waste more.
They will also be less active as would we humans be at higher temp.
If you can keep the temp. for fish down to 30C or slightly less, this will be fine for them.

For corals and some other inverts, they have a much narrower temperature tolerance range,
usually between 22C to 30C.

At these 2 limits, they will not really "die", but they'll be closed most of the time, and over a longer period, will not survive,
especially if they're the photosynthetic type where they need to open up to capture the light.

In most cases, we try to achieve a temp. range of 26C to 29C for corals to do really well.
At these temp., fish will do equally well, so it's the best of both worlds.


Methods of cooling :

1) Chiller using compressors with :

a) externally cooled canisters
- these are average in price for anything from a 2' tank to a 4' tank.
They work on the principle of a copper coil wrapped around a small canister filter,
and having the whole thing insulated with thick rubber.
Water enters the canister and is pumped back to the tank by means of a pump in the canister head.
These are all commercial units made by aquarium eq. manufacturers.

Disadvantage : Very limited and inefficient cooling, since the coil cools the plastic casing of the canister,
and this then only cools the water. For anything bigger than 4', this will be difficult.

b) stainless steel (SS316 preferable)/copper coil immersed in a small sealed glass tank of FW that sits in the sump
- Slightly better than 1a), but cooling effect is also reduced by layer of glass between FW and SW.
However, it can cool larger tanks by simply using a larger coil and a larger compressor.
However, your power consumption bills will be higher than "real" chillers in 1c).
About the same price as 1a), since it's mostly DIY - you can get aircon people to bend the SS coil for you.
Then you'll need a compressor - aircon or fridge type. Then you'll need a sensor that dips into the FW tank
and a digital controller that uses the sensor to turn the compressor on and off.
Lastly you'll need an AC guy to connect up the whole thing for you.
Since the sensor is in the FW, if it reads 26C, it could actually be 27C in the SW.
Some people insert the sensor into a small thin plastic bottle, fill it with FW,
seal the whole thing and drop it into the SW section instead.
|In this case, if the reading in the little bottle is 26C, the actual SW temp. could be 25-25.5C

c) Titanium coil immersed in sump of SW.
Everything else is the same as for 1b) but you don't need the FW tank.
Coupled to a 1HP compressor, can cool up to 1,800 litres. Larger coils will cost more.

d) Titanium coil sealed inside a drum
- called a heat exchanger.
In this case, the drum has a water inlet, a water outlet, and a sealed small hole for the sensor to be inserted into.
A pump in the sump will push water into the drum inlet, and the cooled water will flow back into the sump from the outlet.
The sensor is inserted directly into the sensor hole, which is also titanium, so it sensors the water temp. directly.


2) Evaporative cooling using fans:

This can be quite efficient for smaller tanks, and work on the physical principle that when water evaporates, it cools.
For small tanks, we can use 4" - 5" AC fans.
Forget those commercial aq. fans with 4 or 5 small 2" fans in a row, running off a DC power supply.
They don't have the power to do the job, and cost even more.
For larger tanks like 3', 4' or even more, you can also use exhaust fans like those 10" or 12" units mounted over the tank or over the sump.
Using fans to cool a tank is a lot cheaper than using a chiller, but...

there are 3 disadvantages :

a) Temp. fluctuation can be quite high, since it drops the temperature 2C or at most 3C depending on the surrounding temp. and humidity.
This kind of fluctuation on a daily basis could cause stress in some corals.
To prevent this from happening, you can still use a sensor and digital controller as mentioned in 1b), to control the fan(s).

b) If you have any SW sprays or bubbles in the tank, these could coat the fans and
i) shorten the life of the fan and/or
ii) cause a power-leakage - very dangerous.

Just avoid any air pumps in the tank, do not cause water to splash at he surface (another reason to avoid Overhead filters).

c) Evaporation rates will be super high.
But it has to, since the faster and the more it evaporates, the more it cools.
If you're using an enclosed tank without an overflow system, just use a permanent marker pen to mark the standard water level.
When the water drops below this level, top up using FW or RO water or distilled water, NEVER saltwater, as salt does not evaporate.
If you're using a tank with an overflow system, mark the level in the sump, since the tank level will remain constant.


3) Peltier cooling :

This use a technology developed for PCs using a cooling fan, a huge aluminium heatsink and a Peltier junction to draw heat away.
There is a commercial one in our hobby called the IceProbe retailing in the US for about USD100,
but it's good for only up to a 15G tank (2' X 1' X 1'). It comes with some sort of ceramic rod that's immersed in the water and cools it.
The rest of the device is above water.
Some people install them into Hang-On-Back filters by drilling a hold in the cover and inserting the rod inside.



Handling Evaporation:

Instead of topping up with just water, you can also top up with a frozen bottle of ice,
but without the cap on. This will help to lower the temp. even more.
Just make sure the iced bottle doesn't touch any coral.

If topping up daily seems tedious, you can also build a top-up system.
There are float switches and sensors in the market but these are usually quite expensive,
that control a pump in a bucket of FW to topup the water for you.

You can also use a slow drip method to do the topup for you. Just place a container(s)
that can hold more water than your daily topup volume somewhere above your tank/sump.
Connect an airline tubing and airline valve and insert one end into the container right at the bottom.
Start the siphon, and tighten the valve until the drip is slow.
It is all trial and error to figure out how fast the drip should be, but you can experiment in your basin first.

Another topup device you can use would be a simple ball float like in the toilet cistern.
This is usually used in tanks with sumps, so you can't see the ball !!
You'll have to do some piping either from the water mains or from the same container as in the slow drip method.
If you use mains water to topup, make sure you either connect a filter in the middle with a carbon cartridge to remove the chlorine.
Or when water enters the sump, it MUST by pass an activated carbon section first.

Advantage of 2c) When evaporation rates are high, you can take advantage of this by topping up with KW (kalkwasser)
or a saturated solution of calcium hydroxide, Ca(OH)2 (quite cheap), instead of just FW. What KW does is 3 things :

a) Maintains the calcium level for you. However, if your Ca level has dropped too much, it can't push it up for you.

b) Maintains the KH for you, which in turn prevents your pH from fluctuating.

c) Precipitates phosphates (PO4-) for you, which reduces green hair algae growth.

For KW to be used, you'll have to use the slow drip method, because saturated KW has a pH of about 12.4,
and pouring it straight into your tank will wipe it out.
When you use KW, you can mix about 1 teaspoon in 1 litre of FW,
shake it up properly until you still see some residue left behind. This means that the solution is saturated.
Wait for the solution to clear first before you use it. KW is very unstable, and will react easily with CO2 in the air,
so for the topup drip container, you must have a cover with a hole drilled in it for the airline tube to pass through.
You will need a 2nd hole in the same cover, to allow air to be sucked in when the drip starts.
Otherwise if the bottle is airtight, the KW will not flow.
Also, make sure the bottom of the airline tube in the container is about 1" above the bottom,
to prevent the residual Ca(OH)2 from being sucked into the tank.

Case Study :

For our 2' tank, I would use 2 X 4.5" AC fans mounted on the hood,
spaced about 12" apart, more towards the back(since the lights would be in front),
pointing downwards. Then I'd assemble a topup container for KW additions using a drip valve.




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