How Many Uk Gallons Is This Tank?

[xing]

When referring to tank sizes (such as minimum size for a fish or for stocking guidelines) one always refers to air and glass space. Otherwise it would get very tricky. especially when working out total volume of sumped systems where the sump is at different heights in different chambers.

Otherwise one could go to the nth degree and include the displacement of the glass, the air above, the substrate, any plants, any existing fish, the filter...

I agree entirely with you on this for a general overview re stocking levels, but an allowance should be made all the same (doesn't need to be scientific - just use internal measurements and knock off 5%-10% or so) but it could make a difference when using meds as ODing becomes a real possibility. I don't know what the effects of a 25% OD would be as AFIAK I've never OD'ed. Possibily loss of fish, or maybe the dosing levels err on the side of caution for this very reason

 

[andywg]

I agree entirely with you on this for a general overview re stocking levels, but an allowance should be made all the same (doesn't need to be scientific - just use internal measurements and knock off 5%-10% or so) but it could make a difference when using meds as ODing becomes a real possibility. I don't know what the effects of a 25% OD would be as AFIAK I've never OD'ed. Possibily loss of fish, or maybe the dosing levels err on the side of caution for this very reason

The entire hobby has always based tank dimensions on external sizes. The inch pergallon rule is based on a 180 US gallon tank having dimensions of 6x2x2 on the outside, it does not consider the actual volume of water the tank holds. I severely doubt any medicines are that close to the bone that confusing the external and internal dimensions leads to the medicine changing in its nature.

You will almost never see anything telling you to make an allowance for air at the top of the tank or any other displacement as the whole industry works off of the external dimensions.