Substrate volume and the 10x rule

[Chris_M]

Hi everyone,

I've got a quick question on the 10x rule - why does it work with total tank volume rather than actual water volume? If you have two 60l tanks but one has 10l of substrate in it while the other has 15l, surely it would be logical to have 500lph for the first and 450lph for the second.

It just seems odd to decide how much flow you need without calculating actual water volume.

Apologies if this question has been asked before, I seem to remember it had been but couldn't find anything after a quick search of the forum.

Thanks 🙂

 

[foxfish]

Hi & welcome to the forum - no rules just guidelines so dont worry to much, 8 x 10 x 14 x it really depends of the individual tank.

 

[darren636]

Hi & welcome to the forum - no rules just guidelines so dont worry to much, 8 x 10 x 14 x it really depends of the individual tank.

exactly. i removed 2 massive home grown echinodorus and instantly my flow increased to more than i need.

 

[ceg4048]

Chris,
The 10X rule is a rule of thumb. That means it's made to be simple. We could add all sorts of conditions and constraints to the rule and it would turn into an excercise in computational fluid dynamics. We just want to keep it a simple guideline that takes into account as wide a variety of tanks as possible without going over the top.

Cheers,

 

[Chris_M]

Thanks for the replies guys.

I guess I'm over thinking things with water volume v tank volume - I'm considering getting a tank built to replace my old one and worked out that if I used water volume rather than total, I could add a couple of inches to its length, which is always appealing!

 

[ceg4048]

Hi,
Yes, we don't usually get return value for the effort spent in overthinking, which tends to create more hassles and complications than it solves problems. You'll find a similar inconsistency when it comes to dosing for example. The dosage schemes seen in plans like EI and PMDD often gloss over the fact that the tank typically has 20% or so less water in it than the tank size. So a 10 gallon tank normally only has about 8 gallons of water in it, yet we don't really worry too much about this inconsistency because accuracy in dosing values doesn't offer any advantages in this regard. It's only when we are adding things that are potentially harmful if overdosed, such as medicines, that we need to think carefully about the volumes.

Cheers,