who is good with calculations?

[thesoul2008]

i have 2 tanks measuring (this is water level measurements not tank size)
Length 121cm x Width 37cm x Height 35cm
156 Liters or 41 gallons

The other tank is the same so

156 x 2

313 liters or 82 gallons

my sump measures
Length 121cm x Width 47cm x Height 40cm
227 liters or 60 gallons

so i have to do 108 liter or 29 gallon water changes

so what i need to know is :
I have a Line on my sump a "Full" line for water changes i want to work out how many cm down from that line the 20% water change will be.
i found this calculation on the internet once before but now i cant.

I would like to thank everyone in advance :)

i am guessing it will be something like:

121cm x 47cm x Height? / (1000) = 108 Liters

but i don't know how to turn that around into a calculation :)

Good luck

[Kashta]

Well, I'm not going to do math for you (unless you pay me in beer) :) ... but here's a link to a calculator that will figure it out for you. This one factors in different tank shapes and equipment setup options. Enjoy!

http://reef.diesyst.com/volcalc/volcalc.html

[thesoul2008]

only tells me what i already know :( cant see how i can get the cm measurement i need for water change

[Cluunox]

well if your water depth in the sump is 40 cm and that gives you 60 gl then to remove 29 gl i would bet you need to go to a depth of about 21 cm because you are just short of half the total amount (30 gl) which would be 20 cm. just back yard figuring though. so 40 - 19 = 21cm

[coach_z]

mark your current water line, do a water change (take out 29 gallons), then mark your new line. no math involved. to measure the distance between your two makrs and you find out that you needed to take out # cm of water. then you realize that you didnt actually have to do any measuring at all. or math.

[thesoul2008]

if i can mark cm lines on the side makes it easier for water changes as i loose quite a bit of water each week through evaporation so if i don't do it the exact time every week it will if i can just measure down from the water line it makes it more accurate all the time

[jpappy789]

psssst. there's a calculator at the top of the page...click the conversions link ;)

[SMinNC]

psssst. there's a calculator at the top of the page...click the conversions link ;)

:iagree:

I was gonna point at it too. :)

[Cluunox]

that calculator at the top was what i used : )

[The Zigman]

OK
your 60 gal sump is 40 cm high, so...

60 Gal Divided by 40 cm = 1.5 Gal per cm

so if you want to remove 29 gal from your sump..

29 gal, Divided by 1.5 = 19.3 cm from the top..

make sense?

[petluvr]

Well, I'm not going to do math for you (unless you pay me in beer) :) ... but here's a link to a calculator that will figure it out for you. This one factors in different tank shapes and equipment setup options. Enjoy!

http://reef.diesyst.com/volcalc/volcalc.html
WOW Kashta I would have thought you would have linked the op to an ac calculator ;)
http://www.aquariacentral.com/forums/calc.php

[DGalt]

figure the volume of your sump (121 x 47 x 40 = 227480 cm^3), which holds 60 gallons.

29 gallons is about 50% of your sump. So basically you're going to want to change the water in 1/2 of your sump. Am I interpreting what you're saying properly?

So your line would be 1/2 way down the sump (20 cm below the top). That'll give you about what you want (you can figure it out if you want it to be exactly 29 gallons. 29/60 * 40 = 19.33333333....cm, so your line would be 19.3cm below the top)

don't over complicate things :)

[fwiffo]

i was recallling some volume formulas from calculus myself but was too tired to do them!!!

i would go with zigman's work myself. good enough for what is being done.

[Cluunox]

well if your water depth in the sump is 40 cm and that gives you 60 gl then to remove 29 gl i would bet you need to go to a depth of about 21 cm because you are just short of half the total amount (30 gl) which would be 20 cm. just back yard figuring though. so 40 - 19 = 21cm

my bad i told him what he had left not what he should take out but the amount seems to end up the same.

[thesoul2008]

thanks guys you all seem to come to the same conclusions :) got it pretty much sorted