RO Water Open to Debate!

[phil wood]

Hello

I always use RO with Treated Tap Water only because i was told a long time ago that you should have some sort of mineral content in your tanks.
I know that if i want to bring the KH down to lower the PH you use Ro or by some other means if need be.
But recently i have come accross some people who only use pure RO.
What i want to know from you all out there is do you do the same or do you belive that a bit of mineral content in yer tank goes a long way to the health of your fish.

Please discuss.

Regards

Phil Wood

 

[slimbolen99]

A fellow fish club member used straight RO for his plecos. The problem he ran across was that there were no buffering capabilities in the water, and would experience WIDE swings in pH values. He lost thousands upon thousands of dollars of plecos doing that. That being said, I'm sure it's possible to do straight RO and be successful, although I have no situational experience doing so.

 

[gerald]

Ultra-soft low conductivity water in nature tends to have moderate to high amounts of natural organic matter (from decaying plants and soil), which is essential to fish being able to absorb and keep the ions they need to survive and grow in those habitats. Exactly how that organic matter assists in maintaing ion balance is still mysterious, but several studies with acid-tolerant Amazon stingrays, tetras, cichlids, and banded sunfish have shown they lose ions faster and have osmoregulatory problems in ultra-low conductivity water without natural organic matter. Diet is probably a factor too: if fish can get the ions they need from food, they can probably get by with less in the water. Anyway, I dont see any benefit to using 100% RO (unless your RO unit is inefficient, in which case the water might come out just right!). Pure RO is too demanding on the fish's ion uptake mechanisms and too hard to maintain consistent water quality.

 

[Mike Wise]

To add to the discussion, softwater fish typically don't experience radical pH shifts even in the most softwater biotopes in the wild. The volume of water just doesn't allow rapid shifts in pH or conductivity. Although I use pure RO water for some tanks, it's always filtered through peat first. It pick up some hardening factors, so it isn't really pure RO water.

 

[tjudy]

I think that the only way to get water with ZERO conductivity in a dynamic aquarium is to do frequent 100% water changes with pure RO water. A dynamic aquarium has substrate, driftwood and/or rocks, maybe some plants, fish (obviously) and a well acclimated filter. All of that adds to the solution that is aquarium water. Feeding also contributes. The only fish in my room that are currently getting 100% RO in the changes are the Parananochromis sp., but I only do 50% water changes and also add Kent pH Minus (which elevates the conductivity while reducing the pH).

 

[apistobob]

I use straight RO for all my apistos and have for more than 20 years. That said, I have very complex habitats with substrate, many plants, driftwood and often leaves in all my tanks. I think this environment gives them what they need. The primary reason I use straight RO is that it is the easiest way for me to do water changes. If it was easier for me, I might add tap at times.

Bob

 

[Nebraska_cichlids]

I use straight RO for some of my species (Tilapia joka, Congochromis sp., and a few other species) without any problems. Whenever working with more tolerant species, I add some tap water to reduce the likelihood of large pH swings.

 

[dw1305]

Hi all,

and would experience WIDE swings in pH values

In this case it is the mechanism that we use to "measure" acidity/alkalinity that is the problem, not the water. The swings in pH (in water without any buffering) are largely irrelevant to soft water fish, you can prove this by lowering the pH of soft water with dissolved CO2, you will have gassed the fish long before they are effected by the extremely low pH.

In fact the pH scale is a totally meaningless measurement if you have pure water (H2O), that is water (a solvent) with very few salts (the solutes) in it. The pH will go rapidly up and down as the ratio of acids (H+ donors) and alkalis (also called bases and H+ acceptors). In water with a lot of DOC and humic compounds, these compounds will stop the pH rising, but there is nothing to stop the pH falling rapidly as the CO2/O2 balance changes.

The reason for this is that pH is the measure of hydrogen ion concentration in water. It is measured on a logarithmic scale: a change in 1 pH unit represents a tenfold difference in concentration of hydrogen ions. At pH7 we have equal numbers of H+ and OH- ions (really 2 H2O ~ OH− + H3O+). I'll pinch the next bit from Wikipedia

In a solution pH approximates but is not equal to p[H], the negative logarithm (base 10) of the molar concentration of dissolved hydronium ions (H3O+); a low pH indicates a high concentration of hydronium ions, while a high pH indicates a low concentration. This negative of the logarithm matches the number of places behind the decimal point, so, for example, 0.1 molar hydrochloric acid should be near pH 1 and 0.0001 molar HCl should be near pH 4 (the base 10 logarithms of 0.1 and 0.0001 being −1, and −4, respectively). Pure (de-ionized) water is neutral, and can be considered either a very weak acid or a very weak base (center of the 0 to 14 pH scale), giving it a pH of 7 (at 25 °C (77 °F)), or 0.0000001 M H+

A good way to think of this is as a set of scales, when you are pH7 the scales are balanced and the acid and alkali ends of the scales have the same mass in them, but it doesn't matter what that mass is, pH7 could be because both ends of the scale have 2 grains of "sugar" in them, or a 10 kilo sack of "sugar" in each scale.

In that scenario if we add another 2 grains of sugar to the "acid" end of the "low" scale it will tip towards the heavy end, as it is 100% increase in mass and change in the ratio from 1:1 to 2:1 "acid:alkali", if we add 2 grains to either side of the 10 kg scale it will not change the ratio of "acid:alkali", or pH, at all.

In this case the weights can be thought of as both the dKH, the carbonate buffering and as the amount of solutes in the water, the conductivity or TDS. That is why measuring these tells you much more than the pH does.

These are the "scales" for highly buffered, base rich, alkaline water, where changes in pH really will have a major effects on the inhabitants:

If we leave the factor the same, but make the blocks much, much smaller and tip the balance in favour of "lowers pH" we have the situation in the "nearly RO" water that our fish live in.

For soft water fish if you have a low stocking rate, some DOC and little organic pollution you can use nearly pure RO, and in this case you can ignore swings in pH.
Unless you fully understand the nitrogen cycle, are very conscientious and are very good at water management it helps to have some dKH (I always have some).

I understand that people have had their pH decline rapidly, and at the same time they have had loss of (or damage to) much loved (and often expensive) soft water fish, but I'm pretty sure that the pH decline and damage to livestock are both symptoms of other problems, it is not the pH "crash" directly causing the fish death.

cheers Darrel

 

[Simon Morgan]

Basically, some RO units are better than others. Some will produce <20ppm which is prone to a pH crash, others will struggle to get below 70ppm, but is perfectly acceptable for most fishes including difficult apistos IME. I can get down to 17ppm with my system but I buffer up to 100ppm for general maintenance or 50-60ppm for breeding,
I use a buffer rather than tap water as my tap has v. high nitrates.
Not all ROs produce the same quality water (and it's dependant on tap water too) so it's important to state what the TDS reading is when comparing.

 

[Simon Morgan]

And another thing... because Ammonia is practically non-toxic at low pH it's important not to panic when your pH is below 5 and dump in alkaline buffers. The affect is that the benign ammonium ions (NH4+) lose the H+ and become NH3 again and poison all the fish...

(Darrell, are you getting a deja vu feeling?)

 

[tjudy]

Basically, some RO units are better than others.

The housing of RO units is pretty much the same. There are lots of different arrangements of pre-filters, pressure pumps and what-not that you can add on that will affect performance. But in the end the performance of an RO unit comes down to membrane rejection and effluent ratio.

Rejection... the percentage of solutes that the membrane does not permit to pass through. When membranes are manufactured they are not all the same rejection. They are tested and then rated. Poorly performing membranes (those that reject less than 95%) are sold much more inexpensively than a 99.9% rejection membrane. When you see a sale on new membranes for $30 or less... it is usually a poor membrane. What is the difference? If you have tap water with a TDS of 500 ppm, a 95% rejection membrane will result in RO effluent that is 25 ppm. A 99.9% (there is no such thing as a 100% rating) will produce 0.5 ppm (effectively 0 ppm).

Effluent ratio... the proper ratio of RO:waste water is important for the membrane to function normally. A low ratio (say 1:2) indicates that too much pressure is being pushed to the membrane. More solute will get through and the lifespan of the membrane will be shortened. A high ratio (1:>4) is a waste of water. There is no benefit. The optimum range is a waste water effluent that as 3-4 x the RO effluent. All RO units should have a flow restrictor, which is a capillary tube placed in the waste water line. (http://www.spectrapure.com/St_replac_FR.htm) The length of the tube determines the rate of flow of the waste water. Tuning the restrictor is easy to do. Get two large containers that have measurements on them. I use 1 Liter graduated cylinders. You can also use two milk jugs with lines marked on the sides equally. Start the RO and let it run for a minute. Move both the RO and the waste lines to opposite containers at the same time and clock for one minute. Remove the lines and see what the ratio is. A new RO unit should have a ratio that is too high... this is because the factory has no idea how the unit will work on your tap, so they send a flow restrictor that is really long. If the ratio is not at 1:3-4, remove the flow restrictor, trim off 1/2" and test the system again. Repeat until the flow rate ratio is where you need it to be.

Flushing the membrane chamber.... this is an important component of membrane longevity. I purchased a flush valve that connects to the waste water line. (http://www.spectrapure.com/St_flush_valve.htm) When water runs out of the waste line unrestricted it will flush out any solute/sediment deposits on the membrane chamber that may have gotten past the prefilter. A minute of flush every few hundred gallons is all that is needed.

My 99.9% membrane is almost 6 years old and still produces RO water with 0 ppm TDS. I added a piggy back membrane a year ago so I could double my production. I keep the effluent ratio at 1:3.5, use softened water (from my water softener) because sodium chloride is a lot easier on membranes that other salts, and add a little warm water into the line in the winter (because frigid cold water is not good for membranes either). I also flush the membrane once a week. I used to make 200 gallons of RO every four days. Now I only fill the 150 gallon vat once every ten days or so.

 

[dw1305]

Hi all,

I keep the effluent ratio at 1:3.5, use softened water (from my water softener) because sodium chloride is a lot easier on membranes that other salts, and add a little warm water into the line in the winter (because frigid cold water is not good for membranes either).

Ted that is a very good summary of what you need, the water softener is a good point, a lot of the problems with RO units are because the input water is high in carbonates.

As "6foottank" mentions we've had a similar discussion on the BCA forum, and one thing we found was that a lot of peoples RO units weren't producing water with anything like as lower TDS as they should.

I think that pH, buffering and water hardness are quite difficult concepts to get your head around and they are a recurring motif now a lot more people are using RO. After a quick Google I found I've made a very similar posts on "Planet Catfish", the BCA forum, Plecoplanet and UKAPS, often more than once.

I think this post should be accessible to everyone and I'll post the link to it, because it covers a lot of the relevant points for a specific set of circumstances.

"My water conditions, help, do I need RO or HMA or neither."
<http://www.plecoplanet.com/forum/showthread.php?t=8904>

cheers Darrel

 

[bussardnr]

Ted, how is the piggyback hooked up?