Question Regarding Rodi water and its waste.

[kabe87]

Hi, im new here and before I start my own tank I just wanted to clear my doubts regarding rodi water and waste water.

If I fill a 20 gallon container for water change with rodi and its waste together will it be better than normal tap water?

[gators111]

Yes, but only because you ran it through a carbon filter and presumably a micron filter. The R/O membrane filter essentially did a lot of work for nothing, since you added all the stuff it filters out back with the waste water.

[LizStreithorst]

The TDS will be the same as your tap. Why do you think you need RO? DI is not necessary for Discus.

[DJW]

Well... the answer has to be yes, but look closer. It is better because it has passed through the typical pre-RO stages: the sediment and carbon filters. If you mean to do this as a routine, however, it doesn't make sense to have the RO membranes included in the works, since you are putting everything the RO membranes remove right back when you include the waste water. And the RO part of the filter is the slowest. Do I understand this right? You don't need reverse osmosis unless you are breeding; or you keep wild caught fish and the tap water is on the hard side; or unless you have domestic-raised discus and your tap water is super-duper hard.

I would also remove the deionization canister if it is included as a final stage. When filtering freshwater and doing lots of water changes, DI filtration adds no real benefit and the resin will be depleted in no time at all. It serves no purpose unless you are wealthy and enjoy repacking DI resin every three days.

If your intention is simply to improve the quality of your tap water, you can run the tap water through the sediment filter and the carbon filter into an ageing barrel. If you age and aerate the water in this way then you can do huge water changes anytime you want without worrying about the microbubbles and the pH and all that stuff.

[kabe87]

Thanks for the responses...
Its not that I thought I needed. I used to have Discus and raised them with tap water, then moved on to a reef, bought a Rodi unit and now Im back again wanting to have a discus tank so I thought... I have a Rodi unit maybe I can give it some good use :/

How about adding Rodi water to refill evaporated water? and whenever I have to do a water change I use the waste water made by the rodi unit

[gators111]

You can do that to top off your tank, however, you'll be doing enough water changes that it really won't matter, unless you have some crazy amount of evaporation in your area. I've always kept my discus in reconstituted RO/DI water over the last 14 years, but that's just because I have water that's perfect for African cichlids, not so much for discus. (ph 8.3, tds 235) Incidentally, I use the waste water for water changes on my african tank. And as a side note, my DI cartridge lasts a year and is only half depleted when I change it out.

[LizStreithorst]

You'll be better off if you stick with aged tap for Discus. You will be changing water at least 3 times a week, preferably daily. The evaporation that occurs will not even be noticeable. Discus do much better with stability of water parameters. Save your RO unit for when you decide to breed. Depending on your water you may not even need it for breeding.

[Willie]

My vote is with Liz. Make it easy for yourself to do water changes. That's so much more important than getting the water perfect.

Willie

[DJW]

My vote is with Liz. Make it easy for yourself to do water changes. That's so much more important than getting the water perfect.

Willie

Totally agree. The only reason I take the trouble to make *perfect* water is that my tap water is not any good at all. And I change a ton of water. The main thing is clean fresh water.

[DJW]

... my DI cartridge lasts a year and is only half depleted when I change it out.

A Year? Are you recharging the resin?

This is interesting as it runs counter to everything I have experienced with DI resin. It might be possible for mixed-bed resin to last for a while if you have very soft source water to begin with (hence why use RO at all unless for nitrate), and if you also have no CO2 in the water, and therefore no upward pH swing. The biggest factor in DI resin depletion is the CO2 content of the water. This means that typical well water will go through resin very quickly. On the other hand some city water has no CO2 at all, which would extend the life of the resin.

The devil is in the details. In a RO filter that is working well, the TDS of your RO product water will be about 4-8 ppm. After that the resin would reduce it to 0 or 1 ppm. Thats 3 to 8 ppm going into the resin, and 1000 gallons later the resin in a normal 10 inch can must be spent. It can't hold any more.

Can you describe your tap water and the type of resin that you use? If I could get DI resin to perform that trick on my water I would use it just for the heck of it.

Anyway, the reason that DI has little practical value in freshwater is that, if the RO water has TDS of 5-10 ppm, you will be mixing tap to give it some additional minerals, or you will be adding back powdered minerals. If the purpose of a DI stage is to polish off the last 5 ppm of TDS, why bother with that last little bit if you will be adding it right back?

[gators111]

Not recharging the resin. I've got an Typhoon 3 from airwaterice. I'm on city water with no co2. Water does in at ph 8.3, tds 180 and comes out 7.0, tds 0. Waste water is 8.0 and tds 235. Before it goes to the DI, the tds is 5. As far as the type of resin, it is whatever airwaterice sells. It changes from blue-green to a tannish color. And yes, I use it just for the heck of it since the filter only costs about ten bucks a year. And at the next changing, I'm going to use the old one to fashion a Purigen filter out of it, similar to the reactor BRS sells online.

[kabe87]

Thanks for all the answers, after researching a lot I decided to go with a continuous drip system water change :)

[DJW]

Thanks for all the answers, after researching a lot I decided to go with a continuous drip system water change :)

Good luck with it, and please let us know how it works out. I think continuous drip has the potential to be the best system... its just difficult for most people to accomplish, for lots of different reasons.

[Neptune]

Drip system would be awesome, do you have a drain handy?

[Willie]

This thread is interesting because it illustrates the dramatic difference between reef and discus. I have had many reef keepers ask me about keeping discus, often because they're anxious to apply technology to the water quality problem. I try to explain to them that these require completely different approaches.

In a reef system, much of the technology is trying to take stuff (mostly nitrogen based) out of the water after feeding. It is the ultimate exercise in restraint. Keeping discus is exactly the opposite. Feed them a ton of food then completely replace the water, sort of like slopping hogs. Reef keepers revel in the technology. For keeping discus, you need a heater and a sponge, and an easily accessible water supply.

To each his own, Willie

[DJW]

A wise person once said, "We don't keep discus, we keep water -- the discus just happen to be swimming in it".