How Do You Measure Evaporation?

[dangles]

Just like the title.

I have a gravity-fed ATO setup. I'm curious how others have measured out their evaporation rate. Obviously it will change through the seasons but I would like at least a general idea.

My initial idea is to mark the water level in my sump, shut off my gravity ATO for a few days, then measure how much ATO water I have to put in to get back to that level. But I've noticed that my sump level already fluctuates somewhat periodically so I'm not sure how accurate that would be. The other issue with that method is that I use a kalkwasser stirrer RODI water is getting added from that too - although that's a known quantity of water so I could just subtract that I guess...

Anyway, how have you measured your evap rate?

 

[56longroof]

Why can't you just measure what it takes to fill the ATO reservoir daily for a period of time and average the results?

 

[fishywishy]

I just turn off everything and draw a line at the top of the waterline.

 

[dangles]

Why can't you just measure what it takes to fill the ATO reservoir daily for a period of time and average the results?

It's plumbed directly from my 60 gallon RODI tank :)

 

[wasabi bean]

I am just curious as a relatively new reefer as to why uou need to know evap rates, is it something useful for dosing, i have had a tank for just over a year and know its somewhere in the region of 10l a week

 

[Joe31415]

It's plumbed directly from my 60 gallon RODI tank :)

Without any type of valve to shut it off? Even so, mark the level on the 60g RODI tank today and check it again in a few days.

 

[dangles]

I am just curious as a relatively new reefer as to why uou need to know evap rates, is it something useful for dosing, i have had a tank for just over a year and know its somewhere in the region of 10l a week

I dose kalkwasser using a kalk stirrer. Right now I'm dosing 4.8 liters per night. At some point my nightly kalk addition will outpace my evaporation rate, which. means I won't be able to increase my kalk any more. I need to know about when that happens so I can add in a different method of alk/ca supplementation.

 

[dangles]

Without any type of valve to shut it off? Even so, mark the level on the 60g RODI tank today and check it again in a few days.

Oh of course. I have 2 shutoff valves (one at the sump end, one at the RODI tank). Plus obviously the float valve that I inspect and clean regularly.

That's probably the method I'll end up using. Just curious if anybody had any other ideas.

 

[Joe31415]

That's probably the method I'll end up using. Just curious if anybody had any other ideas.

I'm not sure there are any other ways, at least not for the random hobbyist to do at home*. Mark the tank, stop the ATO, check the level at some point in the future and do the math to see how much it dropped in 24 hours or leave the ATO running and mark it instead.
IMO, it'll be easier to leave everything running and mark the ATO. If you mark the tank, you have to account for the 4.8l of kalkwasser you're adding. While that's totally fine and the math should work, it's going to be more difficult to measure since you'll be measuring such a small change (and through the glass the parallax gets tough to deal with) due to the kalk keeping it someone topped off. The level in the ATO tank should drop more.


*Actually, I can think of a different way, but I'm not sure if it helps you. You could attack this from the other side and treat the situation like you're planning to start dosing. Instead of figuring out about how much RODI it uses, start testing Ca/Alk and when the kalkwasser can't keep up, then you can start dosing.

Sorry, one more, if the kalkwasser is adding more RODI than the tank uses in a single day, you should see the salinity dropping. That could be another sign to watch for. Actually, come to think of it, when that happens, your ATO level will stop moving as the tank won't need it. Neither of these methods will tell you how much your tank evaporates in a day, but they'll tell you when it's evaporating less than the kalk is adding.

 

[dangles]

IMO, it'll be easier to leave everything running and mark the ATO. If you mark the tank, you have to account for the 4.8l of kalkwasser you're adding. While that's totally fine and the math should work, it's going to be more difficult to measure since you'll be measuring such a small change (and through the glass the parallax gets tough to deal with) due to the kalk keeping it someone topped off. The level in the ATO tank should drop more.

I'll probably end up doing it this way. I will still need to account for the kalkwasser though because the kalk stirrer is also fed from the RODI tank. But that's a known quantity so I can just subtract that from the "total delivered" from the RODI tank.