Originally Posted by Gregcoyote
it is based on system volume and livestock load.
Smaller systems it is more economical to use water exchanges, larger systems it is more economical to dose and use methods of nutrient export. Testing is critical if you operate this way. But even in large systems, folks like Mr X still like water exchanges as it is always the simplest way to go. I do minimal water exchanges, but I have a whole room dedicated to nutrient export.
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Couldn't agree more. 25% weekly water changes on a 300g system can get costly. It's better to invest is some nutrient export systems and dosing pumps as they'll eventually pay themselves off with the money saved from water and salt costs.
Then again, depending on whatever system you're running you can always do both. Similar to what I believe Greg here is doing, the occasional water change is always beneficial.
Personally, I like the water change route but if I ever go large, I'll definitely invest in the proper equipment to get a self sustaining ecosystem.