Originally Posted by JDM
Say the fish waste resulted in an increase of 1ppm per day of nitrates (the most pervasive measurable toxin, but it could be anything and it certainly isn't the only thing) and you were flowing 1 gallon per day continuously that would be about equivalent to a 3.4% daily water change.
The nitrate buildup would reach an equilibrium level of 29ppm in 14 weeks. So either you want to up the changing or have a lower production of nitrate. Lots of live plants will do that as they allow most of the ammonia to bypass the whole nitrification process.
Increasing it to 10% reduces the maximum level to 10ppm and 4 weeks to equilibrium.
I considered doing something similar but the tank ended up being located where I couldn't easily feed and drain the water.
Two heaters would be best in this setup, although two in colder environments should be used anyway. I had a recent experience with one heater not providing enough heat for the ambient temperature in the room and a drop in water temp that resulted... other factors were involved but two heaters would have worked better. You are feeding cold water regularly.
I think I see where you are coming from.
Might google... Richard Taylor White paper "Water changing and Nitrate"
Was discussed on another forum ,don't know if paper is still available.
It did discuss continuous flow system's and amount' of exchange needed to achieve desired PPM reading's for nitrates.20ppm = approx 3.5 gal per day or thereabout's.
For me,,, it's easy to hook up pump with hose attached and draw 50% of water from the tank.
Takes about 20 min max,much shorter time than it would take for me to do the math required to achieve the same result's.
My tank's fluctuate with varying fish loads, and food's, so is easier to just change 50% once a week.
Has worked well for a few decade's.(am old and set in way's)
Continuous flow is appealing to me and plan's to once again raise some Juvenile Discus, where frequent feeding's and subsequent water changes are needed to maintain water quality while I am away at work,but I will prolly wait till spring when weather is nicer for shipping fish.