To RO or not to RO...

Andrew D · Jan 10, 2023

I've got a large reef tank and know how important it is to use RODI water for water changes and top-off, but I'm just starting up a large FOWLR and wondered if I needed to start things off with RO or if regular dechlorinated tap water would be fine. I got a report a while back from the local water purification plant and there was nothing of concern identified, but I could always do one of those ICP tests to be sure. Would appreciate some opinions on this please. System will be about 600G's and hold angels, butterflies, triggers and large tangs. Thanks in advance. Andrew

MERKEY · Jan 10, 2023

Your inhabitants will appreciate RODI

If you have thebmeans I would do it.

Sounds like a simple 4 stage would be just fine and those are fairly inexpensive compared to the amount of fish you are talking about.

thatmanMIKEson · Jan 10, 2023

Andrew D said:
I've got a large reef tank and know how important it is to use RODI water for water changes and top-off, but I'm just starting up a large FOWLR and wondered if I needed to start things off with RO or if regular dechlorinated tap water would be fine. I got a report a while back from the local water purification plant and there was nothing of concern identified, but I could always do one of those ICP tests to be sure. Would appreciate some opinions on this please. System will be about 600G's and hold angels, butterflies, triggers and large tangs. Thanks in advance. Andrew

Yes always go r.o!!! Lol. I would definitely invest in a r.o system and storage with a system volume that large.

I evaporate over 2 gallons a day with less than half that volume.

bushdoc · Jan 10, 2023

Well, people were running FOWLR tanks on salt mixed with tap water. My first FOWLR was established in a rental apartment without possibility of RODI system.Landlord early agreed for Aquarium.
I would by minimum, though use RODI for top-off although with size of your system if you choose to buy it from LFS it will brake the bank( and possibly your back), so better to get your own RODI system.

CoralB · Jan 10, 2023

Personally I would use RODI water if your financially able .

Tamberav · Jan 11, 2023

I would use RODI just to try and keep algae or diatoms and uglies down. I know FOWLR has lower lighting but pest algae doesn't seem to need a lot.

AydenLincoln · Jan 11, 2023

RODI all the way some affordable units exist…anything but tap water especially if it’s U.S. tap water. If not RODI you can use distilled or buy pre-made water from your lfs and if they don’t sell it Petco does or you can buy it online.

JC1977 · Jan 11, 2023

I actually was using tap water treated with prime the last couple of months on my 180 gallon fowlr after reading and talking to a guy at my LFS about tap water in fish only systems being ok. I don’t have any hard evidence that the tap water was detrimental but I did notice the diatoms and algae etc on my glass is starting to come back faster and thicker than normal and a few of my fish are acting abnormal like twitching during copper treatment. I haven’t tested like I said but the eye test is sending red flags so I’m switching back to ro/di water with a 50 gallon water change this weekend. I get it’s a 600 gallon system and it would be convenient to just use tap because that was my reasoning but I’m with everyone else here it’s just not worth it to cut a corner here.

thatmanMIKEson · Jan 11, 2023

JC1977 said:
I actually was using tap water treated with prime the last couple of months on my 180 gallon fowlr after reading and talking to a guy at my LFS about tap water in fish only systems being ok. I don’t have any hard evidence that the tap water was detrimental but I did notice the diatoms and algae etc on my glass is starting to come back faster and thicker than normal and a few of my fish are acting abnormal like twitching during copper treatment. I haven’t tested like I said but the eye test is sending red flags so I’m switching back to ro/di water with a 50 gallon water change this weekend. I get it’s a 600 gallon system and it would be convenient to just use tap because that was my reasoning but I’m with everyone else here it’s just not worth it to cut a corner here.

diatoms are showing up quick, tap water is full of silicates and more than likely chloramines that prime can't touch. Tap is not the best for living aquatic life, and it could hurt your chances if you ever want to go reefing down the line.

vetteguy53081 · Jan 11, 2023

Andrew D said:
I've got a large reef tank and know how important it is to use RODI water for water changes and top-off, but I'm just starting up a large FOWLR and wondered if I needed to start things off with RO or if regular dechlorinated tap water would be fine. I got a report a while back from the local water purification plant and there was nothing of concern identified, but I could always do one of those ICP tests to be sure. Would appreciate some opinions on this please. System will be about 600G's and hold angels, butterflies, triggers and large tangs. Thanks in advance. Andrew

I used to do the tap water as I have only run large tanks and started to see hints of cyano and having a 5 stage unit reassured me it was pure laziness on my behalf. Tap alone has ingredients such as chloramines, lead, zinc and others and just not worth it . water conditioners such as Prime will dilute certain elements but not remove them.
RODI is the way to manage water which is the lifeline of all our specimens in the tank