another RO/DI question

[apexifd]

this probably been asked before. but, I am going to asking again.

I am planning on ordering an RO/Di system from aquasafe this month for both fish tank and drinking water.

and I notice the home system only has 1 DI canister while the aquarium kit has 3. What are the difference of having 1 vs 3?? effect on drinking or fish?

thanks

Peter