Skimmer rating ?

I'm not sure what you are trying to say.

 

Do you mean by increasing flow rate though the sump you will decrease bioload? This is not the case. Bioload is directly related to the size of the tank and it's inhabitants. Factors like filtration, water flow, treaments, RO/DI water quality do play their parts - but the size of the SYSTEM and the type/number/size of the fish are the two biggest factors(note: BIGGEST - not only) when determining bioload.

Since increasing the flow rate through your fuge will not affect the volume of the system nor the ammount of "stock" in it - you will not be decreasing the bioload in this manner IMO.

 

He's trying to say that "skimmer A" might be rated for 100-200 gallons; 100 gallons if the tank is heavily stocked, 200 gallons if the tank is lightly stocked.

 

I guess i was trying to say the skimmer rating is based on a fully stocked dt. Any water you have in sump/fuge is not adding to bio load. In this case a 90 gallon heavy bio load skimmer should suffice. Most people (myself included) would probably go up a size. Perhaps it was a moot point, after all it's only 20 gal difference. Sorry if i added to confusion.

 

The amount of fish we can have is determined by the amount of dissolved O2 the water can hold. That is determined by salinity, altitude, and temp.... and of course how much water we have. So most folks consider the total water volume for such limits, and most folks will stock to that limit. So it is best to go by heavy load. (the majority of folks probably overstock)

If you have a 90g tank loaded with the proper amount of fish.... then you add a 100g sump.... you still have 90g worth of fish.... the load the skimmer needs to remove is the same. It has not gone down... you just have more water. Most folks do not shop for a skimmer based on a 90g load in a 200g tank and call it a light load. I suppose you could... just not that common.

People that actually want a light load to keep a ULN system and only have a few fish will still probably have a powerful skimmer for their tank.... even though the load is light. But those folks are not real common and they are going for a specific tank and know what they are doing.

And M-Ocean is right that actual water volume of the OPs sytem will only be around 90g so no need to look for something rated for a 120 or 240g. 90g sytems are super popular and tons of skimmers are suited fine for that range.

It's probably semantics and we are talking about the same thing... you just through me when you said "adding water outside the DT lowers bioload. " Biolad is the same, it has not changed.