Using RO waste - caution

[Tommo]

I've noticed that a number of members here use RO waste water for growing on fry etc. However, a word of caution needs to be noted in this regard. How many of us really know the composition of the 'raw' water we are passing through our RO unit?

An RO unit normally has two prefilters: a 5 micron (approx) filter to mechanically remove waste and a carbon filter that removes some 'chemical' impurities. The RO membrane then filters out approx 99% of the other 'stuff' giving us 'dead' water which we can safely adjust to our various needs. The waste water therefore, is a concentrated soup of god knows what? Check the TDS of your tap / raw water and compare it with the TDS of the waste water. The waste will be significantly higher . . .

I'm not saying that using RO waste is necessarily bad per say - only that we need to know the composition of our raw water before using this soup in our aquariums. But, I hear you say, the water has been prefiltered through carbon? In this regard we also need to consider a number of other variables: the frequency that we change the carbon prefilter, the quality of carbon used and also the limitations of its use in removing certain undesirable additions from the water supply e.g. as far as I'm aware carbon cannot remove chloramine?

Food for thought I hope?

[Moon]

I learnt this the hard way. I was using RO waste for all the grow outs. One day I lost two tank full fish. I found out the cause to be RO waste. I have way of testing the constitution of the waste water. But did experiment with a smaller tank full of regular plecos. Lost the entire tank as well.
Lesson learnt. Now my waste goes to the garden.

[Second Hand Pat]

Joe, do you ever figure out what was in the RO waste causing the problem?
Pat

[JamesHe]

I just treat it as tap water. add Seachem prime to it.

Normally, the RO/Waste ratio is 1:3 or 1:5. so the concentration is higher by 33% or 20%, that is it.

[nc0gnet0]

As I was responding to this thread I realized you were refering to those that use pure RO waste water for growouts, and not those of us that only add a portion of the ro waste water back to the pure water to get out TDS levels where we want them.

I am still a bit skeptical, if the RO waste water is bad, then the tap water itself is marginal at best. RO waste water is only about 1/3 higher in dissolved mineral content.

[Moon]

Joe, do you ever figure out what was in the RO waste causing the problem?
Pat
Don't really know Pat. The water tested OK for ph and hardness. There must have been some contaminants. I am on well water and it does go through an inline softener.

[Keith Perkins]

Rick, you should ask Paul (pcsb23) about this. He might convince you.

[Tommo]

As I was responding to this thread I realized you were refering to those that use pure RO waste water for growouts, and not those of us that only add a portion of the ro waste water back to the pure water to get out TDS levels where we want them.

I am still a bit skeptical, if the RO waste water is bad, then the tap water itself is marginal at best. RO waste water is only about 1/3 higher in dissolved mineral content.

All I’m suggesting here is that members consider the possible adverse effects of using RO waste water. You say that you are ‘still a bit sceptical…’ I believe that this can only be a good thing although I would rather use the word cautious. When people start talking about TDS readings I wonder how many of them actually know what Total Dissolved Solids are? Many people think that they are simply measuring the mineral content of the water – if only that was true life would be so much simpler . . .

TDS readings are a useful guide and no more – great, for example, to check whether your RO membrane is still functioning efficiently etc. You say that your water is only 1/3 (33%) higher in ‘mineral’ content than your tap water – that may, or may not, be true using the water from your suppler. I would however, suggest that the water supply from other locations could show higher or lower comparison readings. It is also vitally important to recognise that TDS also measures / includes other ‘solids’ e.g. the presence of heavy metals etc will increase TDS readings.

You also say that ‘if the RO waste is bad, then the tap water itself is marginal at best.’ Again this may or may not be the case. I once lived in a house and had my tap water tested in a laboratory and the phosphate readings were very high! We also have to consider that what is deemed satisfactory / or safe for human consumption doesn’t necessarily mean that it is safe to keep our fish in. Think of some of the additives that water companies are putting into our mains water: chlorine (easy to remove) now being phased out in some areas in favour of chloramines (more of a problem to remove), the addition of fluoride to protect our teeth, the use of aluminium sulphate as part of the filtering process and so on. These all contribute to the simple TDS readings that the ‘average’ aquarist doesn’t even consider. TDS measure more than mineral content . . .

Thank god for RO units as they remove 99% of these ‘solids’. However, the key question is what is left in the waste water? And that is the whole point of the discussion – we don’t know what is in this ‘soup’ unless we have our source water properly tested in a laboratory.

[Moon]

I totally agree.

[brewmaster15]

Everyones RO waste water is different as far as its composition. I tried raising fry from various cichlids here in my Ro waste water and there was never any good results...The fry would stress and darken and die....my source water is well....tap water is fine here for raising fish...but RO waste water is definetly not good for my fry.

I know some have great success with it, I attribute that to their source water not being overly high in something that when concentrated by the RO unit becomes toxic.

JMO,
al

[John_Nicholson]

Like Al said it depends on your location, but I have used for a very long time without any issues. In fact I am using it currently.

-john

[nc0gnet0]

Just to clarify, I was talking about adding a small portion of the RO waste water back to the RO water and not using total RO waste water. If you can raise/keep Discus in your tap water, then this practice is fine. However, in Moon's case, I would care to guess that him being on a well and having high phosphates makes his well water itself unsatisfactory or marginal at best for keeping discus. In this case I would not advise using any RO waste.

Long story short, if your tap water is safe for discus, then adding RO waste to up the TDS level of your product water should be fine.

Rick

[nc0gnet0]

You also say that ‘if the RO waste is bad, then the tap water itself is marginal at best.’ Again this may or may not be the case. I once lived in a house and had my tap water tested in a laboratory and the phosphate readings were very high! We also have to consider that what is deemed satisfactory / or safe for human consumption doesn’t necessarily mean that it is safe to keep our fish in. Think of some of the additives that water companies are putting into our mains water: chlorine (easy to remove) now being phased out in some areas in favour of chloramines (more of a problem to remove), the addition of fluoride to protect our teeth, the use of aluminium sulphate as part of the filtering process and so on. These all contribute to the simple TDS readings that the ‘average’ aquarist doesn’t even consider. TDS measure more than mineral content . . .

Thank god for RO units as they remove 99% of these ‘solids’. However, the key question is what is left in the waste water? And that is the whole point of the discussion – we don’t know what is in this ‘soup’ unless we have our source water properly tested in a laboratory.

While everythig you said is true, you didn't make a case to support your claim emphasized in bold. If your phosphate levels in your tap is high, then it is as I said marginal at best.

[Tommo]

While everythig you said is true, you didn't make a case to support your claim emphasized in bold. If your phosphate levels in your tap is high, then it is as I said marginal at best.

I thought the case that I was making that in the example of 'phosphate' in the tap water agreed with your proposition that: yes, in some instances, water quality can indeed be marginal. The only case I'm trying to 'support' is that we as aquarists should be, in your words, 'skeptical' in my words 'cautious' when following advice from other members who advocate using RO waste for whatever reason . . .

The amount of aquarists who think that TDS simply measures the mineral content of water is very high and we, I hope, have a responsibility to correct this notion. Give people the full facts and then they can make an informed decision on whether of not to use RO waste. That was my only reason for starting this thread.

There are also far easier and safer ways to increase mineral content than using RO waste - e.g. by adding magnesium sulphate (epsom salts).