# Reverse osmosis and chemistry :)



## dominic (Feb 28, 2006)

Hi,

I'm sure I've read a load of informative articles over the years about RO units, and how to get the product water into a 'fish/plant friendly' state.

Now that I've finally gotten round to buying an RO unit for a tank that (I think) is going to be a discus tank, I can't find anything at all.

I must be using the wrong search terms.

Anyhow can anyone point me in the direction of some good articles on this?

Things I'm interested in are:

- What to add to the water to raise/buffer the pH (particularly since CO2 injection will be used)
- I bought a TDS meter with the RO unit, but I'm not really sure what the 'meaning' is other than a measurement of the ions in the water - What level should it be at? What should I use to increase the level in product water and what will this do for the plants and the fish?
- I know that I've read somewhere that raising TDS doesn't raise KH or GH (maybe faulty memory though! ). How should I raise these?

I know there are products out there like Kent's RO-Right and Seachem's Equilbrium, but I'd really like to understand a lot more about the interplay of the KH, PH, TDS, and GH and which chemicals affect each. Ideally I'd like to take a 'PMDD' like approach to preparing RO water rather than just blindly buying pre-prepared stuff. Feel free to tell me I'm mad though 

Finally, I know there's a lot of information on this stuff out there, so apologies if this is a daft question. I'm just having difficulty finding it all.

Thanks


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## Laith (Sep 4, 2004)

I'll try to answer some of your questions...

Buffering is done by the KH in the water (GH has no impact on pH buffering). You should have around 3 to 4 degrees KH in order to have the water safely buffered. KH can be added using baking soda (sodium bicarbonate) which will raise the KH without touching GH. Remember, this should be baking *soda*, not baking powder.

GH is a measure of the Calcium and Magnesium content in water. GH can be raised using a combination of CaCl2 (Calcium Chloride) and MgSO4 (Magnesium Sulphate). These chemicals will only raise the GH and not touch the KH.

I'd aim for a KH of 3 or 4 and a GH of 6 to 8.

Seachem's Equilibrium is an excellent product for RO water (I've heard it's much better than the Kent RO Right product though I've never used it) and adds Calcium, Magnesium, Potassium and some Iron. It does *not* add any KH.

By the way, two comments re the use of RO water:

- Why are you wanting to use RO water? Most plants and fish can live in a wide range of tap waters, unless you want to breed specific fish or have high levels of metals etc in your tap...

- Another way to prepare RO water is mix it with tap water to get the desired KH and GH. Just find the right ratio.

I'm not an expert in TDS but it is not a measure of GH. There is a correlation between high GH and high TDS but TDS measures all dissolved solids while GH is mainly a measure of the Calcium and Magnesium. A good use of a TDS meter with an RO unit is to be able to check when to replace the membrane: a new membrane will yield water with extremely low TDS while a clogged one is indicated by the processed water getting a higher and higher TDS reading.

Hope this helps. Do searches on Calcium, Magnesium, sodium bicarbonate, Equilibrium and you should get lots of detailed info and dosing recommendations.


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## Salt (Apr 5, 2005)

Laith said:


> I'm not an expert in TDS but it is not a measure of GH. There is a correlation between high GH and high TDS but TDS measures all dissolved solids while GH is mainly a measure of the Calcium and Magnesium.


This may be how many people regard "GH," however, it's not accurate... GH and TDS are really the same thing.

"GH" is an abbreviation for *g*esamt*h*ärte, which is German for "total hardness." It was deceided that it is best to keep the German abbreviation of "GH" instead of creating a new English abbreviation ("TH" for total hardness), and to find an appropriate English word that begins with the letter G. The best fitting word was "general," so that's what was used. However, this really isn't accurate, it's *total*.

GH is intended to be a measure of exactly what it's supposed to be - TOTAL hardness. This includes ALL dissolved solids in the water.

When you test GH using EDTA (which for quite a long time was the main way of testing GH), all of the dissolved solids will not react. The top two ions which react are calcium and magnesium. The rest don't react much at all unless they are in great concentrations. Since the main dissolved solids in tap water tend to be calcium, magnesium, and carbonates, "GH" as it has come to be known in the USA is a measure of calcium and magnesium ions, since for all practical purposes, those are the only ions that show up on the EDTA chelation tests.

Since the advent of accurate testers which test the conductivity of most all ions in a given water column, TDS or "Total Dissolved Solids" is now a true representation of the water's actual "gesamthärte."


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## Laith (Sep 4, 2004)

Yes, you're correct in your observations.

However most people are using the term GH in relation to what their test kit tells them. Aren't current GH test kits still using EDTA? so they're measuring mainly Ca and Mg.

A TDS meter will measure true total hardness, not just Ca and Mg. Therefore I wouldn't say that a TDS of xxx is equivalent to a "standard" GH reading of x degrees.

Or can you?


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## dominic (Feb 28, 2006)

Thanks for the replies.

The main reason I bought the RO was to provide suitable water for the Discus (water where I live is hard). And nearly everything I'd read on discus said that they *must* be kept in softwater (this was the last time I read up on them a few years back). Having done more reading this time (though after having bought the RO), the opinion seems to have shifted to suggest that discus only *really* need soft water for breeding. Some guy on the UKDA forums who has been keeping / breeding discus for years have been using raw tapwater - didn't even use water conditioner - water straight from the tap (and they live practically next to the water supply plant where they were using chloramine) - He said that it didn't affect the discus at all - he further said that he'd never use RO or water conditioners.

Anyhow, now that I've got the RO, I guess that I'll be able to provide water closer to Discus preferred composition. Maybe mix the RO water with the 'waste' water (which I assume should just be tap water with chlorine removed).

For all my other tanks, I've just been using conditioned tapwater without any problems.


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## niko (Jan 28, 2004)

Some observations about using reconstituted RO:

For my water changes for about 2 months now I have been using RO water with added dry:

- NaHCO3 (baking soda, very little to get the KH to 1, raises/buffers pH)
- CaCl2 (to GH=3)
- MgSO4 (traces, part of the chlorophill molecule, a must have element)
- K2SO4 (to about 20 ppm)

Basically all the ingredients of Seachem Equilbrium but from different sources.

I don't check TDS but it is best to keep it as low as possible. A low value for a fertilized tank wiht regular water changes is 250. Keeping it lower than that would be difficult with the salts that the plants need.

In the course of the 2 months, in my 3 tanks, I started noticing is that the plants gradually starve. It happens very slow - I guess some of the chemicals that were in the tank from before the "reconstituted RO phase" are being gradually exhausted. I have the feeling now that reconsituting RO is not perfect for plants. I cannot say how good it is for discus.

I will start using my usual 70-80% RO + 30-20% tap water mix. Yes you can use the waste water from the RO system, it has no chlorine and it's not that dirty anyway.

--Nikolay


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