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What are your thoughts on RO - RO/DI water for freshwater planted tanks?

RO - RO/DI Water

4391 Views 18 Replies 10 Participants Last post by  Edward
Whos using it, who's not, what are your thoughts? Pros, cons....
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-Used it with tap water and it helped
That would be my vote. Alone, R/O units don't help at all (need to reconstitute water). My tap water has changed recently so I only use the unit for toping off. I like to have control over my water parameters, others feel like it's to much work. I used to use R/O tap water mix on a 20 gallon, anything bigger might be to much work.
Use it due do to unstable well water.
RO is fun

I use RO for several years and I like it. It gives me the option to control all the elements.
With tap water we never know what is going on. There could be ions of high concentrations that we have no test kit for.

Last time I tried tap water the snails looked dead for a week.

There is no issue with the operation cost. The whole system needs one $3 10 um cartridge and one $10 carbon cartridge a year. The cost of running water is $1 for 60 gallon of pure water. The main cartridge works for 5+ years.

This mix I use, is to recreate balanced levels of Ca2 and Mg2. This is used for a long time, since DI was introduced to breed Discus.

3.0 g CaSO4
1.0 g CaCl
1.5 g Soda
1.0 g MgSO4

Final concentrations can be tested by TDS meter for breeding or by regular Calcium test kit for growing aquatic plants.

Thank you,
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Well it's been a month now since I have posted this poll and about 2 months since I started using RO/DI myself. It sure is very nice to be able to control water parameters to your liking and experiment with different levels in different tanks, it also makes killing snails very easy by lowering your GH and KH to the point where their shells become weak and brittle. But most of all I have noticed in general that my tanks are cleaner, spot algae is less than what it used to be so that is nice. The biggest advantage is probably to the fish in my case as my tap water has heavy metals in it which do a great job at killing my fish if I use a water conditioner that does not treat for heavy metals, I found that out the hard way. Now I don't use any conditioner at all.

I bought my 100gpd filter from aquasafecanada (ebay seller) for around $150 with the 3.2 gallon container (a must IMO), shipping and a digital TDS meter. That's quite cheap and based on what I hear about replacing filters, the only one that really costs a lot is the RO membrane and DI filter, both of these have a nice long life span and in 4-5 years I'm not sure if I'd spend $80 on new filter elements or just buy a new unit from them again, price difference is not a lot if you think about it (excluding the TDS meter and 3.2 gallon container). Plus I now have very good tasting water and ice cubes :)

Considering what I spend on my tanks each year it's not very difficult to justify $150 on pure water.

Giancarlo Podio
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good to hear you like it.

The TDS is a great thing to have, but the DI is not necessary for planted tanks and for drinking, as it makes water really unstable. Also the container may get infected with microorganism at one time. UV sterilizer makes it perfect safety combination.

For drinking use, filtration over coral makes it valuable add on. One day you get bored by the plain taste of RO, 1/4 teaspoon of Sea salt per gallon makes excellent taste and healthy source of drinking water.

Thank you,
It is my understanding that while RO water is prefectly safe to drink, DI water is not. I do not have facts and this is only something I seem to have dug up from some deep dark recess of my own mind. Since my RO/DI has a takeoff to bypass the DI unit, it's no big deal to fill a gallon jug to keep in the fridge, but gosh it would be nice to add an ice-maker and run it off the RO/DI.

So is RO/DI, safe to drink?
Good question. I think it's a much debated topic, you hear both sides of the story anywhere you go. I've been drinking RO/DI for a couple months now and am still standing :)

I think most people will save their DI filter because it doesn't last long and regular RO water is more than sufficient for drinking. If I see my DI filter doesn't last long I may do the same myself. I'll look more into the DI issue just in case I shouldn't be drinking it...

Here's the exact same unit that I purchased on ebay for 1/4 of the price:

Here's a thread on the drinking topic:

Giancarlo Podio

I'm curious why you add CaCl and CaSO4.

I too use RO/DI and it is simply for the control it gives you.
In light of the DI debate and if it's safe to drink or not, I figured it's not going to hurt to remove it out of the loop. A quick change in a couple tubes here and there and I now have RO coming out of the tap installed on the sink for drinking purposes and RO/DI out of the auxilary hose under the sink for my tanks. Besides removing any possibility that the DI may cause some unwanted side-effects, this should preserve my DI filter and extend it's life considerably. Luckily these filters use quick disconnect hoses and it's real easy to change things around and re-configure the entire filter to your liking.

Giancarlo Podio
Art_Giacosa said:

I'm curious why you add CaCl and CaSO4.
I used to breed discus before plants took all my free time. First, there was an ion exchanger DI, made of cati and ani to purify the water. I still have HCl hydrochloric acid and NaOH sodium hydroxide at home. These were needed to regenerate the functionality of the DI. From this experience, I know how unsafe DI is to maintain and to drink.

The water purity produced by a DI is 10x better then the distilled and 100x then the RO, but it doesn't matter for the plants.

DI, cati/ani 0.1uS TDS
Distilled 1.0uS TDS

Back to your question, waters stripped of minerals need to have restored basic living conditions for the fish eggs to develop and for the fry to survive. It's all about balance of salt ions, causing osmotic pressure on living organism. Balance of Ca:Mg:Na:Cl. This is why I am still using the discus breeding formula to grow aquatic plants. If it's good for discus, must be good for plants. And it works just fine.

It's a mix of dry minerals:
3.0g CaSO4
1.0g CaCl
1.0g MgSO4
1.5g Soda

For discus keep adding until desired conductivity uS TDS is reached. For plants until measurable Ca2+ .
For an automatic continues RO water change, this kind of dosing makes it difficult to keep stable levels. So I started experimenting with dolomite as Tom Barr suggested. It is a mineral made of CaCO3 calcium carbonate and MgCO3 magnesium carbonate. . This dolomite might replace the discus formula for plants if it proves to be working.

Thank you,

2005 01 05
Dolomite increases TDS and KH too much. Ca and Mg is there, but the KH is out of control.
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I'm planning on setting up my old 20g long as a reef tank, and will need the RO setup. I'll probably go with the small ones, around 25g/day or smaller, so I should have enough for my other FW tanks.

Until then, I'm fine with using tap water in my FW tanks.
I have used RODI water for years in my Saltwater Reef tanks,only thing you can use.
Trace elements are added after and plus the addition of the kalk drip kept ph steady at 8.00 to a high of 8.3 during the day.

I think I might try a 50/50 mixture on the Fresh water aquarium to see if the algae and ph will get stable.
Another question on this has anybody tried a little sea salt to combat Alage?
I have to use it in my area...well *some* may argue that, but the tap water around here is approx:
ph= 8 - 8.2
kh/gh = 21-22 dKH/dGH
I use RO/DI to cut with tap. My tap is super hard so I have to cut it 2 parts tap : 3 parts RO/DI to get my water at 4kh 8GH. My DI is getting killed, I just replaced it a month ago and it is already turning colors (showing the need to replace it) Do you guys think I can get away with just using RO? Will RO only water have any measurable GH or KH? Thanks
Hi Jason

There is no point using DI for planted aquariums. The RO cartridge already removes 90 – 99 % of all dissolved elements. Here is how it works:

500 uS TDS very hard water
300 uS TDS usual tap
10 uS TDS RO
1 uS TDS distilled water
0.1uS TDS DI

RO water does not have any GH or KH. You need to either mix it with tap water or add Ca, Mg and KH. Plants need Ca and Mg for healthy growth.

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Thanks for the insite Edward!!
I have an RO/DI unit that I am currently using for both my fresh and salt tank. I want to switch back to tap for my FW because I plan on stocking it a little more densly with plants. Currently I have Java moss and Fern which really don't care what they are immersed in. My tap gives me a TDS of 160 ppm, which looks about half of what Edward stated for his tap.
Hi robitreef

There are two TDS systems, ppm and uS.
uS = 2 x ppm
ppm = uS / 2

160 ppm = 320 uS

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