Preventing Microbial Growth

[SantaMonica]

I need to select an RODI system for infrequent use. My setup will be a continuous water change that changes one gal per day on a 90 system. The RODI will be filling up a 30 gal brute container once a month; salt will then be mixed, and then the automatic part will slowly use that water over the next 30 days.

Problem is, I've read about microbial fouling of the membrane if the RODI is not used more than once per week. Well, I can't use it once a week, because once the 30 gal is made and the salt is mixed, it must emptied before I make a new batch (in 30 days).

So, will my system work with one of your units?

[BuckeyeFS]

Any/all RO and RO/DI systems should be used at least once a week, regardless of the brand name.

That said, there may be an aspect of adding water to your aquarium you've not considered.

In general, purified water is used in two ways with a marine aquarium:
1. Water changes (water is removed periodically [once a week to once a month or so] from the aquarium and replaced with "new" salt water).
and
2. Top offs (purified freshwater is added to the aquarium to make up for evaporation).

The system you describe has evaporated water being replaced with saltwater. You'll find that this process will adversely increase the salinity of the tank water.

You can use the daily need for top off water to trigger frequent (at least once a week) use of the RODI.

You'll not want to set up a situation that has the RODI constantly cycling on and off every time your sump level drops just a small amount. This can happen if folks plumb the system output to a float in their sump.

If you'd like to discuss in greater detail, feel free to call in: 513-312-2343.

Russ

[SantaMonica]

Actually this is separate from the RODI top off, which will be operating also. The top-off is easier, since new RODI can be added to the holding container anytime.

But the continuous water changer is a seperate container that has a pump which pumps one gal a day into the tank (a separate pump also takes out one gal a day.) Since this container is for 30 days, it is 30 gal. Since salt must be mixed, new RODI cannot just be added anytime; it must wait for the 30 gal container to empty so that a new fresh batch of saltwater can be made.

[BuckeyeFS]

Maybe I'm missing something. You'll set up your RODI for frequent use (top off water), and also use it to make 30 gallons at a time once a month. That sounds like a workable approach.

[SantaMonica]

No, it will be set up to only make water once a month: 30 gal for salt, and 30 gal for top off. The 30 gal salt container will be filled and mixed with salt, and the other 30 gal container will be filled and mixed with kalk. Then, each of the two containers are drained slowly (one gal/day) as they are used up.

While it would not kill it to add to the freshwater more often (this would just dilute the kalk), it is preferable to not have to do this, since the whole design is to be hands-off for 30 days.

[BuckeyeFS]

Unfortunately, you'll not find an RO membrane that is intended to by used in that way. You'll likely have trouble with the top portion of the membrane drying out and with biofouling in portions of the system exposed to nonchlorinated water.

Manufacturers wince a bit at use only once per week, but in practice folks have luck with a once a week regime.

Rather than 30 gallons, I suggest you size your top off tank at about 1.1 times your weekly evaporation, and refill it at least once per week.

Russ

[SantaMonica]

Not sure the weekly routine will work for me; that was the reason for designing a monthly one.

I've heard that maybe using a UV on the RODI inlet would keep the bacteria out, thus extending the time between needing to run the system. But what about the "drying out" you mention?... if the system stays connected (except of course for the inlet being turned off for a month), are you saying that air will still get in?