10:20 There are equations we use for this in wastewater engineering. What you want to know is what is the exiting massflow of contaminants. For comparitive purposes, you can assume a value for the generated contaminant mass in a given tank in that week. (Some fraction of the incoming food mass [a portion exits the tank as CO2 from respiration and the rest has fate of fish bodymass, dissolved solids, and suspended solids. Most of what you care about is the dissolved solids])
So adjust the equations for a batch reactor. Simple enough in this case, the equilibrium state if you water change the same amount every week is that the massflow out of the system as dissolved solids is equal to the portion of the added food mass that does not become co2 or become suspended solids (exit when you clean the filter and includes contributions to bacterial biomass solids from other categories).
Unlike the waterchange, the drip system follows the kinetics of a complete mix continuous flow system, so the effuent concentration of contaminants in the tank at all times and the massflow out is the concentration in the tank multiplied by the flow-through volume in the same amount of time. In General, this means that it takes alot more water changing to maintain the same minimum concentration in the tank, however for waterchanges that only change a small fraction of the water volume, increasing the frequency of these approximates the same kinetics as the continous flow system.
The most water efficient system is to change nearly all of the water infrequently, but we care more about labor efficiency

Thank you for sharing!  This gives me some ideas on how I might want to run my own auto drip system.  Very well thought out and clean setup.

Thanks for the great idea. I am currently doing my research on this to setup for my tanks as well. Your video was very useful.

Thanks so much! Making a fish room so you really helped me out!

Just got this system working this past weekend for my 135 gallon aquarium.  Since I already use a (plexiglass) sump filter, I put the output there instead of in the aquarium so I didn't have to drill the aquarium glass (which is about 1/2" thick). I had always wondered how to do automatic water changing, but couldn't come up with a really good way to do it.   Your design is very elegant and worked great for me, once I got some help for the harder parts.  Thanks for posting this!

Very nice system! Thanks for sharing.

Thanks for sharing! I have one last tank to drill and then I'll be setting up my system

So the water change happens by inflow of clean water into the aquarium causing the water level to rise and drain out of the tank? How do you know when to stop, ie, how much waters been changed?

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Hello ya waiting for this!

Nice system!

Great videos/Great content/Great advice/Great set/subscribed

Good work bro

Aweosme video!! I wish I could edit videos like you! I made my own auto water change system similar to yours but i don't do a drip I run my water thru a thermostatic temp regulator. Then I turn it on with my wyze sprinker app and let it run for my desired time. i really like your setup! i need to make a video of my system and post it!!! Good luck!

I would consider getting a ph doser controller if you're not on rain water...

8:24 I wonder if your drip emitters would clog less if you upgraded your RO system to 7 stage RO/DI bringing your TDS down to zero? Your sediment filter looks pretty dirty.

I wonder if an inline heater could be installed somehow on this?  

Great system btw 🎉

Hii thank you for making this video where are you located? Man I want this system!!

What are the parameters of your tap water?

Can anyone tell me what the fittings are at 5mins and 7 mins, I'm also looking for the fitment that has a screw cap on it so I can ads bleach to the drain...any info would be great, great vid too