Backyard Aquaponics
A place to discuss aquaponics

Hey guys iv been running two IBC systems for a few months 1 at my place and one at my parrents place only iv notist they need to be refilled regularly.

The water level drops aboud 10CM per month in both IBC systems (just the standard IBC setup with one IBC)
My question is this normal? i suspect that the valve on the bottem could be leking.

Or is this just usual water usage from the plants and evapation?
If it is leking is there a way to fix it? both systems have been put in the ground so you cant access the valve unless you dig the hol thing up...

Hi Njord,

I'd say it's most likely due to evaporation through the media and transpiration of the plants as they are likely to be in a sunny warm position. 100mm/30 days= 3.33 mm drop per day. My bio pond drops 6-7 mm per day in summer.
If you want to make sure the valve will not leak empty the container and silicon the inside of the valve and silicon a bung into the outlet.

Pete.

I'm adding about 15% top off water per week during the summer for my systems. I don't know if that's normal, it seems kinda high but I can't find any leaks.

One decent size tomato plant will use 4 litres a week
That's why I have a ball float valve to keep mine toped up

Calculating "normal" is a doable thing... but perhaps figuring it out empirically would be easier. If you put a protected tub (no dogs drinking from it, no rain entering, etc.) near your tanks that you know doesn't leak, and you carefully measure the amount of water it contains over a period of time, I'd expect its evaporation rate to be pretty similar to your tank's evaporation rate and you could see if they both jive with each other. The evaporation rate is influenced by the temperature of the water at the surface, the humidity of the air, the area of the water surface and the temperature of the air, as well as air flow. One of the evaporation rate formulas is:

g = Θ A (x₁ - x₂)

where...

g = amount of water evaporated per hour in kg/h
Θ = evaporation coefficient in kg/m²h (25 + (19 x air velocity at water surface in m/s))
A = water surface area in m²
x₁ = humidity ratio in saturated air at water temp in kg/kg (kg of water in kg of dry air)
x₂ = actual humidity ratio in the air in kg/kg (kg of water in kg of dry air)

To simplify this, find a good table or calculator for figuring the (x₁) humidity ratio in saturated air ratio for your temp, for example, using this one at TLV: Calculator: Saturated Humid Air Table, given a temp of 21.5ºC, what they call Absolute Humidity, shows 16.1551 g/kg. For our calc we convert that to 0.0161551 kg/kg humidity ratio in saturated air at 21.5ºC.

The actual humidity ratio in the air can be determined from Relative Humidity which is commonly provided by the weather prognosticators using a Mollier Chart (same as a rotated 90º and mirrored Psychrometric Chart) to cross-reference the dry air temp with the Relative Humidity:

Or even easier, use an online MOLLIER DIAGRAM CALCULATOR as so nicely provided by AFIM Dehumidifying (Thanks guys!) to find that at, for example 50% Relative Humidity (adjust the Barometric Pressure if need be) the Absolute Moisture is 7.967 g/kg, converted for our calc to 0.007967 kg/kg actual humidity ratio in the air at 21.5ºC and 50% Relative Humidity.

If the Area of your tank is 1.2m² the only thing left to figure out before you can calculate the Evaporation Rate is the Evaporation Coefficient based upon Wind Speed: 25 + (19 x air velocity at water surface in m/s). In still air, that would be: 25 + (19 x 0) = 25. With Wind Speed of 18 km/h (or 5 m/s) that would be: 25 + (19 x 5) = 120. How about let's go with Wind Speed of 5 km/h (1.39 m/s), so: 25 + (19 x 1.39) = 51.41 for our Evaporation Coefficient.

So, our formula is: g = Θ A (x₁ - x₂)

Θ = 51.41
A = 1.2
x₁ = 0.0161551
x₂ = 0.007967

g = 51.41 x 1.2 x (0.0161551 - 0.007967)
g = 51.41 x 1.2 x 0.0081881
g = 0.5051402652 kg/h

If you had still air that would be:

g = 25 x 1.2 x 0.0081881
g = 0.245643 kg/h

Note how big a difference a little bit of wind can make...

If we can assume that 1 kg of water = 1 liter of water (please! please!) then we've got an evaporation rate range above of from 0.25 lph - 0.5 lph. Is that reasonable?

Let's see... Lots of little bitty numbers and calculations to make calculations... How about let's assume zero evaporation at night and something in the middle of that range (0.375 lph) for 12 hours per day. So that would be...

0.375 lph x 12 h = 4.5 liters/day out of an IBC tote. That would be 31.5 liters/week and 135 liters/month.

That seems to be reasonable. It is much lower than dstjohn99's 15% per week, but he is likely talking about higher temps in the Summer plus his fish drink a lot of water, and it is around what Petesake is talking about at roughly 135 mm/30 days in a 1000 L IBC. Throw in the variables of plant transpiration that F&F is talking about and I think the calculations seem reasonable.

Does that make sense? Lots of constantly moving variables there! If anyone has the time and inclination to double-check those numbers, I'd greatly appreciate it!
Way past time for a cold one after cooking my brain a bit too much thinking about evaporation rates!

--
Sam

you can go Sams way (and get an incorrect answer - see below) or go with the F&F wisdom ... simple answer is that you are just coming out of summer and evap will be quite high so losses of 10cm are not unreasonable and will vary a bit depending on what you are growing and how dense..

those European heat waves wont have helped (chuckle chuckle - what heat say the Aussies).

for IBC 10cm = 100L per month is basically a bucket a week - not much at all if air temps are 20 C and above.

the main factor to check which can lead to preventable loss is the depth of water in your grow beds.
if the water is too close to the surface then it will evaporate too easily. If 5cm [ or 2" ] or greater the top of the media will act like a mulch.

If the media is wet at the surface you are wasting water.


if you had a leak, unless just droplets at a time, it is more likely that you would be losing a lot more water.
But as you are going in to winter - if a leak and water still drops 10cm when temps <15-20 C then it may be a leak..... as you have buried the IBC not really any quick fix, normally you can put some form of plug in the outlet valve pipe. Plus unlikely your IBC's would leak at same rates.



[edit] Sam - you provide an equation for open water evaporation (evaporative flux).
It does not apply to agricultural usage. It only provides an edicative potential evaporation
ie. the equivalent of "pan evaporation". There would have to be a plant species, growth rate,
soil moisture and irrigation efficiency factor built in to the equation.
The text book solution is to use something like the Penman-Monteith or a variant
using the pan evaporation as evaporative potential Ep.
However P-M etc were developed for open field dirt agriculture and would be less applicable to
intensive horticulture like hydroponics or aquaponics.

Most high yielding plants and trees use > Ep. Yep - plants use more than Ep.
(is a 2D versus 3D thing and relates to the total root access and net surface area of leaf stomata)

Not my way! I'm 100% for auto-top ups with ready water. Anyway, there were several folks wondering what was normal and maybe comparing evaporation from a nearby tub relative to water loss from the big tanks would identify a problem with water loss in the system somewhere. Or perhaps it would confirm that the experienced water loss is within normal expectations. The real problem with trying to estimate or calculate or even guess evaporation losses is that there are just TOO MANY variables even in fairly tightly controlled environments.

--
Sam

love the emoji - with modification it could be pee ponics......

anyway - as per my [bloated] post above - I suspect lack of depth of water below media (too wet) is probably a factor for the OP beyond plant use. Pretty common issue.

Hi F&F,

with what water do you top up? Degassed town water, other water? I was thinking of using using a float to deliver town water to a tub with a baffle and let the degassed water drain out the other side into the IBC - what do you think?

Pete.

Just town water from the tap not degassed
Nothing special the little bit that goes in May be 1 or 2 litres a day Easley mixes no problem

F&F,
In an earlier post you warned me against using copper in a FT as a heat exchanger.
Doesn't delivering water through the float valve via copper pipe have the same issue? Or is it the direct contact to the fish that's the issue?

Thanks, Pete.

Plain water is ok its the fish water that must not contact copper
Don't know why just its what's floating around and everybody goes by it

Town water is buffered* and monitored so that it won't dissolve/erode any metal pipes or fittings it goes through and leach metals into the supply. Aquaponics water often contains salt, and nitrification drives the pH down; this provides the conditions necessary for leaching to happen, and you start getting dissolved metals building up in your system water, where they'll kill your bacterial colony or poison your fish (depending on the metal in question and what concentration they build up to).

So yeah, having (town) water delivered into the system through a copper pipe will do zero harm so long as the pipe in question isn't dipping into the system itself. Metal in contact with the water needs to be stainless steel and/or coated in some way.

(* For anyone who's wondering about how bad things can get, this is what happened - and is still happening - in Flint, Michigan. Their water supply got switched from a fairly pure source to a cheaper one that comes from a catchment area where road salt is used in winter; the people in charge chose not to spend money on the legally required treatments that would have prevented the salt in the water from causing problems; the salty, corrosive water immediately started stripping lead and other metals out of the old pipes in the town, and now that the pipe surfaces have been damaged even switching back to the old source wouldn't stop the contamination. Metal + unbuffered/untreated water = bad things happen!)

Thanks for the clarification Mel & FF.

While thinking about the possible reasons I recalled a product called Coppercote which is used to coat boat hulls so as to minimise the growth of barnacales by killing them with copper oxide that leaches out of the paint. Ships were clad with copper for the same reason.

Interestingly, stainless steel doesn't oxidise underwater and will corrode below the water line if uncoated which is one of the reasons it's not used for boat hulls. May be titanium will be ok....

Pete.

Tnx for the info guys:)