[repharaoh]

How can I create an extremely slow drip, like only 5 gallons per day?

I want to do a continuous water change system on a 40 breeder. I'd use a 0.5GPH drip irrigation emitter for 12g/day on a 100g tank; but I need less than half of that, and they don't make drip emitters that slow.

It has to be nearly maintenance free and reliable. I don't want to worry about a flood if I go on vacation for a week. I guess maybe a needle valve might do it?

 

[ytro]

Bulk Reef Supply has a doser that has a 1.1ml/minute flow rate. You could hook that up to a timer and it should do what you need it to. They are well-made, moderately priced and have a 2 yr warranty.

 

[Bandit1200]

I don't know how you plan on supplying the water, but if you wanted to go the drip irrigation route, use the smallest one (0.5 gph) and add a timer to the setup and figure out how many hours a day it needs to run at that rate. I haven't done drip irrigation before, but I do use the Rain Bird irrigation timer hooked up to a soaker hose in the garden and it's awesome, especially down here near the coast where we see 90+ temps from June - October. I use this one:
Rain Bird 1ZEHTMR
It allows for a maximum run time of 6-hours with up to 2-start times per day, so if the math for that doesn't add up to your total, get a bigger emiter or pair of the smaller ones and dial it back in the time.

 

[ichthyogeek]

It sounds like you want an automatic water changer. Look into auto dosers which should be able to get you to that 0.5 gph mark that you said you wanted.