Rules of Thumb-Water Volume

[ccombs]

Our industry loves to have rules of thumb based on how much water you have in your tank. Everything from percentages of water for a water change, to how big of a tank you can have for your fish. My question to you is this- do you go by actual water volume in the tank, or what the tank can hold?

For example, I have a 30 gallon tank, but in reality with the equipment, rocks, sand, etc. it has closer to 20 gallons of water actually inside it. That being said, if you were religiously sticking to 10% water changes every week, would you do 3 gallons (tanks total volume) or 2 gallons (water actually in the tank).

Same goes for fish, in my situation of a 30 gallon tank, would you put fish in that are good in a 30 gallon tank, or would you stick with smaller fish that are best suited for 20?

I have my personal opinion and will reveal that later, I just want to see what all you guys think!

 

[TriggerFinger]

For dosing, medicating and stocking I would go with the actual volume. Don’t think it would matter with water changes.

 

[Aardvark1134]

1) You do water changes because they need to be done not because of some rule of thumb. Every tank has different loads and different filters and this will effect water changes. Some tanks can go very long times without a change. Others need one almost every week.
2) Fish should not be stocked by volume of the tank. A 8x2x2 240 Gallon can hold very different fish than a 38 inch cube which is also 240 gallons.

 

[Billdogg]

I start figuring out appropriate dosing numbers by guesstimating the actual volume including sump. For that I'd rather start a bit low and increase as needed. I don't medicate my DT at all, just my QT which, because it has pretty much nothing in it but a heater and some PVC, allows me to better judge the actual volume.

Stocking is so dependent on not only the size and shape of the aquarium but also the amount and type of rock that IMO each needs to be judged accordingly.

 

[Tamberav]

1. doesn't matter....I just change whatever amount is needed to keep the tank clean and parameters acceptable. Early on that meant 5g a week (of a volume of about 15g after accounting for rock). Now I do 5g every other week. May cut it back to 2.5g. The tank is maturing and coral growing....it just doesn't need that much water changed anymore.

2. For dosing I go by actual volume of water in the tank...so early on I dosed based off 15g when using a calculator but now have it dialed to where I can just increase the dosage a bit as consumption continues to slowly rise.

3. For fish I go by dimensions...Territory and swimming area. Volume doesn't matter to me.

 

[Hermie]

I use actual water volume but I only estimate it
I figure in a 23 gallon, I have 20 gallons of water and in a 10 gallon sump I have 7 gallons of water, so instead of 33 gallons (nominal) my system is 27 gallons (of water).