Salinity monitor driven ATO

[nematoad]

So, I have been reading up a lot on ATOs, and it seems all of them either use a float switch or a optical sensor to monitor water level.

 

But to me, this makes no sense, as water spillage can cause the water level to decrease without changing the amount of salt in your aquarium. Essentially then, you are lowering your SG for no reason.

 

I'm surprised to see that there aren't any ATOs operated or controlled by a salinity monitor. Any reason for this?

Does anybody have an ATO that is driven by a salinity monitor?

[Matty1124]

do you have bunch of money to spend.... i would venture to guess this is the main reason people have float switches and optical sensors opposed to salinity/SG probes which would need calibration

 

how often is water spilling out of your tank that a float switch would cause a problem like that? and what would happen if water did spill out of your tank with a salinity monitor? it would still only have RO water to replace it still lowering your SG... and if it didnt come on then your pumps would run dry

[VDub90]

I think the biggest reason is cost. A salinty monitor is a fairly expensive piece of equipment. And in reality there shouldn't be that much water spilling out of the tank.

[Sac_State]

So, I have been reading up a lot on ATOs, and it seems all of them either use a float switch or a optical sensor to monitor water level. Water spillage can cause the water level to decrease without changing the amount of salt in your aquarium. Essentially then, you are lowering your SG for no reason.

 

why would your tank be spilling enough water so that it lowers the tank's water level enough to set off a float valve? that's the real question!

[Urchinhead]

From an engineering perspective its a more complex solution. Complex because you would a conductivity probe, a way to monitor the input from that probe, logic to interpret the values being sent from the probe, and logic that would facilitate an action based on the interpretation of the input.

 

An ATO unit is a binary state machine. If value of switch == 1 then turn on power to ATO pump. If value of switch == 0 then turn off power to ATO pump.

 

From a cost perspective the salinity solution is allot more too. You need an expensive probe and more complex (and thus more expensive) circuitry.

 

With the ATO its just a float switch and a on/off switch in essence.

[nematoad]

Ok, so bad example with water spilling out. But hopefully some of you got the point.

 

I suppose it is an expensive piece of equipment, but it wouldn't be that much more than having a pH controlled CO2 system on a planted freshwater tank. And really, if a controller was say $200, and the low volume water pump was something like $50, you're still looking at a very precise system for an ATO that isn't crazy expensive. Certainly less expensive than many water pumps and lighting options.

 

The only drawback I can think of maybe is that the salinity probe needs recalibration every few weeks causing a slow drift in SG, but I'm sure that's something that can be overcome somehow.

 

And if the control is an issue, they already have pH and ORP units that control solenoids to control CO2 and O3 (ozone) input, so I don't see how using a salinity probe is too complex to program, given it would only have to control a water pump

 

and what would happen if water did spill out of your tank with a salinity monitor? it would still only have RO water to replace it still lowering your SG... and if it didnt come on then your pumps would run dry

 

If you had a salinity based controller, a loss of water volume not by evaporative means would not activate the controller, as the SG of the reduced volume would not change. If you did it purely volumetrically, if you were to scoop out some water (or say, remove a piece of LR, thus lowering the water level), you'd activate the optical or float sensor, getting RO pumped in inappropriately.

[VDub90]

I'd be curious to find out how much water needs to evaporate to go for a change of say 1.026 to 1.025? It could be enough water that the tank could be to low. As it is now the ATO in my tank tops up less than a quarter cup at a time. The water level in the tank is almost immeasurable the amount it changes, where as say the salinty difference may be an inch of water level. But who knows?

[nematoad]

That's what I'd like to know really. I'd think that a large drop in water (large enough to cause the ATO to activate) would definitely have an effect on SG, especially in smaller tanks where a smaller amount of evaporation has a bigger effect. Do you need a small drop in water level (.5 cm) to get a .001 change in SG in say, a 10g standard tank? Or is the drop larger (1 - 2cm) thus being beyond the point of where an ATO would kick in anyways?

[Aliasnumber1]

They are inversely porportional. Say your sensor is in a back chamber of a 30 gallon (113562 mL) tank that by some chance you siphon out of and you remove 500mL or about 1/8 gal. Then your ATO starts, and refills that volume. The other facts are 35ppm or 35 grams per 1,000,000 grams of water (1 gallon) is what most people run their tank at ignoring the fluctuation w/ temp.

 

In this scenario (C1)(V1) = (C2)(V2)

C1 is the concentration at the time immediately before the pump starts and equals 35ppm

V1 is the volume immediately before the pump starts and equals 113562 - 500mL = 113062mL

C2 is the concentration after the pump refills 500mL, and is our variable we're solving for

V2 is the full volume = 113562

 

C2 = 34.84ppm

A change of 0.16/35 = 0.004 or 0.4%

 

Second example, if a 5.5gallon tank 16x10x8 drops 1" before an ATO kicks in

16x10x1 = 160/231 = 0.69 gal.

(35ppm)(5.54-0.69 gal) = (X)(5.54 gal) ; X = 30.64

[nematoad]

Second example, if a 5.5gallon tank 16x10x8 drops 1" before an ATO kicks in

16x10x1 = 160/231 = 0.69 gal.

(35ppm)(5.54-0.69 gal) = (X)(5.54 gal) ; X = 30.64

 

Thanks for the calculations (really, no sarcasm), but your equation is wrong.

 

The smaller volume (lower by 1 inch, or 0.69 gallons) occurs in the latter (c2v2) side of the equation since the evaporative loss makes the volume lower and increases salinity after evaporation, making the difference:

(35ppm)(5.54 gal) = (X)(5.54 gal-0.69 gal)

X = 39.99

 

So your SG after 1 inch of evaporation in a 5g tank is 1.030 (~40 ppm). If you're having sensitive inhabitants, the slow swing up in salinity may not have a huge effect, but certainly the sudden jump down in salinity when the ATO kicks in after 1 inch of evaporative loss is a large change (1.030 down to 1.026).

 

All in all, I'm not really challenging using float valves or optical sensors, as it's tried and true and works well for larger systems. I'm just saying to keep things more consistent in smaller tanks, I think a salinity controller on an ATO would be so much better. Somebody needs to make one, or I need to lear how to make my salinity monitor into a controller.

[Jahms]

So your SG after 1 inch of evaporation in a 5g tank is 1.030 (~40 ppm). If you're having sensitive inhabitants, the slow swing up in salinity may not have a huge effect, but certainly the sudden jump down in salinity when the ATO kicks in after 1 inch of evaporative loss is a large change (1.030 down to 1.026).

 

In a 5g tank, one inch is a lot of water, if I had a 5g tank i'd set the float switches about half a centimetre away from each other so the water is always constant anyways which yields a constant SG.

 

I don't know though, It seems like you are trying to take a simple system and make it much more complicated, it IS a very cool idea though.

[nematoad]

I don't know though, It seems like you are trying to take a simple system and make it much more complicated, it IS a very cool idea though.

 

I'm just thinking, if we can monitor SG/salinity on a real time basis, and not just from evaporative loss, then why shouldn't we take advantage of it?

 

Also, it's just using a different system to control the ATO. IMO, since salinity is what we're aiming to keep constant, why not base it on salinity, not volume which correlates to salinity (assuming the initial volume has the desired SG).

 

Just an idea. Although I think it would be a pretty good one if brought to practice.

[Aliasnumber1]

I was solving for the splash in both situations, and giving you the formulas and constants to do whatever you need. Sorry for the confusion. The equation is right, though.

[czim]

In the first post, an optically controlled ato was mentioned. I was wondering if anyone could link me to one as all the units i've seen are magnetic floats.

 

Thanks

czim

[neanderthalman]

I'm just thinking, if we can monitor SG/salinity on a real time basis, and not just from evaporative loss, then why shouldn't we take advantage of it?

 

 

Well, here's one reason why....

 

If the cost (in dollars and effort) outweighs the benefit, then it's not sensible to take advantage of it, even if we can do it. This is why most people have not bought into clearly superior blu-ray. It might be better, but it's not "better enough" to justify the cost over standard DVD....

 

IME, float switches typically used tend to turn on at around 1/8" of evaporation, which is more than enough for even the smallest tanks. The expense and complexity of setting up a salinity based unit is massive compared to a few bucks for a pair of floatswitches and a relay. Also, when an analog signal is used, the probability of failure of the probe becomes much higher. The cost of the probe makes having a backup or triplicated voting logic prohibitive. A backup floatswitch, on the other hand, is a couple of bucks and requires no substantial change to the design

 

People tend to use the design because it's an easy DIY, it's cheap to get the parts and troubleshoot, and the performance is more than adequate. It's easy to modify the design to make it fault tolerant and robust, and you can tailor it to your specific setup.

 

Not every mousetrap is in need of reinvention, but if you're more interested in the challenge than the final result, then this would definitely be a project worth tackling for the thrill alone. If all you want is your tank topped up, then stick to the floatswitch based DIY or buy an off-the-shelf solution.

 

The optical ATO is the tunze osmolator. Great unit, but pricey. There may be others, but I have yet to see a DIY version.