Help with RO

[topline]

Hi All

Have just ordered myself a RO unit. Its on this page..

http://psifilters.com.au/Reverse-Osmosis-Laundry.htm

under the Aquarium heading (PSI-020A).

I went for this unit as it has dual TDS meters and a bypass valve to mix RO and filtered water together to get desired TDS.

My question is...

Should I add just pure RO water (constant drip, 10%/day) until desired TDS is reached in tank and then adjust incoming water to suit, or should I set the unit to desired TDS and then wait for tank to catch up?

1st option would take about a week to get to TDS of 50, second option would take MUCH longer.

Thanks in advance
Brian
Perth
Australia

[Diana]

Much better to take longer, especially when you are aiming to go so low. I would set up the unit to some halfway point for a few weeks, then set it lower.

What is your current TDS? Maybe plan on cutting it in half over a period of a couple of weeks or more.

Constant drip of 10% per day sounds good, but I would not use straight RO.

[topline]

Thanks Diana

kH currently between 7 and 8.

Cheers
Brian

[Diana]

KH of 7 or 8 degrees suggests TDS is high, too, but is not an accurate measurement of TDS.

If you drop the KH by not more than 1 degree per 24 hours this MIGHT be safe for most fish, but fish adapt slower to softer water than they are used to. It is easier for them to handle changes that occur with rising TDS.

Go SLOW. I would rather see this project take a month, and you still have all your fish, rather than pushing the change to go faster, and ending up with stressed or dead fish. If you dropped the KH by 1 degree per week, I am sure that this would be safe for all the fish that can handle such a low KH. (don't do this to Rift Lake Cichlids, for example )


What kind of fish are you making this change for? Breeding Discus? Rams?
A TDS of 50 is REALLY low. Be extremely careful to monitor all the water parameters. There is not really enough minerals in this water to keep the nitrifying bacteria thriving. They prefer a GH and KH closer to about 3-5 degrees, and a pH closer to neutral or slightly alkaline.

[topline]

Thanks Diana

Correct me if I'm wrong, but 3 german degrees is roughly 53 TDS??

Will reduce hardness gradually as suggested.

Fish List
Clown Loaches 6-8.5 inches
Satanoperca
Geophagus
Uarus
Severums
Yoyo's

Am interested to see changes in cichlid breeding behaviour at low TDS and acidic conditions.

May, in time, even try very acidic conditions (very slowly) to see if Satanoperca eggs will develop and also see if clown react favorably...

Cheers
Brian

[Diana]

German Degrees of Hardness is used for carbonate hardness (KH) and general hardness (GH). 1 Gdh = 17.9 ppm (part per million, same as mg/l)

My TDS meter is adjusted to report the changes in conductivity as if it is all being caused by salt (Sodium Chloride). It also reads in ppm. It may not be perfectly accurate for fresh water tanks with no added salt, but at least it gives me a consistent number to match when I am doing water changes.
A little more questionable when I am trying to match store water that comes with a new fish (Store does add salt) so I can set up a q-tank.