How Big is Your System (Really)?

Bret · Apr 12, 2023

Many of us describe our system volumes by the advertised volume listed by the tank/sump manufacturers, but the actual volume is always somewhat, or significantly less.
Tank sizes are usually listed based on the outside dimensions, not taking into consideration the glass thickness and running water height, let alone the volume taken up by the rock, sand, equipment, or even livestock. Generally this isn't a big deal and is industry standard, but how many of us use this volume when dosing or adding supplements or doing water changes? How many of us are significantly over dosing additives?
I recently took down one of my systems that consisted of a standard 29 gallon display with a 20 gallon sump. 49 gallon system volume, right? Not even close! I measured the water volume I removed at ~26 gallons (of which 10 gallons was in the sump). Typically when I estimate my system volumes, I ignore the sump capacity and just go with the display volume to approximate my actual water volume, but I was still over estimating by about 10%

Do you consider actual system volume when adding supplements/chemicals/etc. to you aquarium?
How are you measuring actual system volume?

mjw011689 · Apr 12, 2023

I was curious about this when I was starting my 90 recently. 90 gallon with center overflow and either 15 or 20 gallon sump (can’t remember offhand). Anyways, once I put 80 pounds of sand, and 2 Liferock reef trees which they say are around 30-35 pounds each, my tank and sump combined only took 85 gallons of water (exactly). So tons of displacement really. Over 20 gallons worth

WarChief · Apr 12, 2023

Bret said:
Many of us describe our system volumes by the advertised volume listed by the tank/sump manufacturers, but the actual volume is always somewhat, or significantly less.
Tank sizes are usually listed based on the outside dimensions, not taking into consideration the glass thickness and running water height, let alone the volume taken up by the rock, sand, equipment, or even livestock. Generally this isn't a big deal and is industry standard, but how many of us use this volume when dosing or adding supplements or doing water changes? How many of us are significantly over dosing additives?
I recently took down one of my systems that consisted of a standard 29 gallon display with a 20 gallon sump. 49 gallon system volume, right? Not even close! I measured the water volume I removed at ~26 gallons. Typically when I estimate my system volumes, I ignore the sump capacity and just go with the display volume to approximate my actual water volume, but I was still over estimating by about 10%

Do you consider actual system volume when adding supplements/chemicals/etc. to you aquarium?
How are you measuring actual system volume?

You got me wanting to go home and take some internal measurements to verify volume now!!

paragrouper · Apr 12, 2023

When I filled the tank, I put 26 gallons of water in.

This is the number I use

Troylee · Apr 12, 2023

It took 320 gallons to fill my 400 gallon system.. so I go off that..

EricR · Apr 12, 2023

Best I can do is use some online calculators that take into account best guesses at rock displacement but I, really, have no idea what my true volume is.

It'd be interesting to see a database of info from people that actually paid attention to true water volume when first filling different tank sizes.

Signalhead · Apr 12, 2023

on my system I have a 150 gallons plus 40 at the sump. I go by 150. I took about that much to fill the system.

o2manyfish · Apr 12, 2023

After updating our display tank last fall, we put all the plumbing under the patio. When that trip to Home Depot came back at $600 I calculated how much water we had sitting inside the pipes underground and the volume was 46 gallons.

My tank capacity volumes is 1500gals but the filled volume is 1250.

Dave B

ReefinIt · Apr 12, 2023

It was always a guessing game so when I set up my last tank, I measured the volume I put in. Tank is 130g, 48X24x26 with an external overflow box, 40 gallon breeder sump, and a good amount of rock. I put in 128 gallons.

vinvinaa · Apr 12, 2023

Can I simply calculate the display tank volume without factoring in the sump volume?

vtecintegra · Apr 12, 2023

48L x 24H x 29W, 3/4" glass with a significant amount of rock took 100g to fill.

mrpontiac80 · Apr 13, 2023

I actually measured my water volume by gallons when I recently upgraded tanks.
my tank is a 180 gallon external overflow with a trigger systems triton 44 sump.
All said and done, after rock sand and etc, my system holds 187 gallons running..

ca1ore · Apr 13, 2023

How, exactly, does one measure the amount of water required to fill a system LOL. I just take the ID measurements (in inches), multiply them together and divide by 231. My 450, with 1" walls held 400 gallons. That most tanks hold much less than advertised has been long known.

steveschuerger · Apr 13, 2023

I’m running a 60 gallon IM AIO so assume I actually have roughly 50 gallons in the display. Have a small refugium hang on so total system volume is about 63 gallons

EeyoreIsMySpiritAnimal · Apr 13, 2023

A standard 90 gallon holds about 79 gallons with nothing else in the tank...

OscarHaglund · Apr 13, 2023

I have a red sea reefer 300. Going by the external dimensions it is 284l plus sump. Funnily enough i measured the amount of water i added when filling it up to be ~280l including the sump. This is with rock and sand.

Pankney72 · Apr 13, 2023

250 gallon custom tank filled close to the top with a moderate amount of rock. 70 gallon sump filled about 75%. I just call the system 250 gallons for most purposes. I do water changes though, so other than cranking up or down my calcium reactor I rarely have volume based measurements to make.