RO Water TDS levels? Too low bad for fish?!?

I recently purchased a ro unit and was wondering if the membrane was working properly. So I've purchased a dual inline tds monitor which is suppose to tell me if the membrane is functioning effectively. My question is what should the the output or product water tds be for me to safely use for my reef tank?
From what I understand if the feedwater is 200ppm then your product water should be 10-20ppm, or 90-95% rejection rate. But I am very confused by a statement the tds company makes about salt water aquarium use of ro water:

"A constant level of minerals in the water is necessary for aquatic life. Changes in the amounts of dissolved solids can be harmful because the density of total dissolved solids determines the flow of water in and out of an organism’s cells. Concentrations that are too high or too low may limit the growth and may lead to the death of many fish or reefs.

A level of 400ppm or less is recommended for most freshwater fish although many softwater fish demand a significantly lower level. Conversely, saltwater fish require a very high level of anywhere from 5000 to 50,000 ppm. Total Dissolved Solids are also important for proper osmotic regulation, which is the relationship of water versus dissolved solids in the cells and the external environment. The greater the amount of solids in the water versus the solids in the tissue of the fish will result in a fluid loss via the gills."

If this is the case using ro water with a tds of 10-20 ppm would be toxic!?!?! Someone please help me understand this!!!!

 

no its the other way around. Its easily confused, so no worries I thought the same thing.. Original TDS needs to be as close to 0 as you can get.. This is to prevent adding more nutrients or heavy metals to your system that come in the local water.. It is true that the TDS in the fish tank will be much higher.. In fresh there are nutrients floating around and the same for salt, but in salt you have dissolved salts, and other heavy chemicals dissolved.

 

Hi, correct me if i;m wrong but
From what i understand, by using reef salt for your tank you are already giving them all the TDS that they require. potassium, borate, magnesium, calcium etc. These and many other elements are what you referring to that the fish require to stay healthy.

The TDS that you receive from your water supply however is a different story. it may contain other minerals which are unnatural to marine life, i.e. silicate, FE and so on. That is why you water your product water to be as pure as possible ( the salt mix will take care of the rest).

 

you are completely correct. I use reef salts very successfully for this reason.. My TDS from my RO/DI is 0, and Im sure my TDS in the tank is in the thousands.. I wouldnt worry about in tank TDS, I dont think anyone really checks theirs..

 

You want control and know everything that goes into your tank. By using a RODI unit you take your tap down to 0 TDS. Clean slate, and then you put all the essential minerals back in when you mix up your artificial seawater.

There are trace amounts of copper, lead and other harmful elements in most tap water. Corals and inverts are sensitive to and can be harmed by these elements if they accumulate over time.

 

I can easily see how the company's statement confused you. It is both correct and misleading at the same time. The easy way to view their statement is to think about what would happen to your fish if you moved them from your reef tank into a tank filled with water straight from your RO/DI (that's fresh water, no salt). You are right that it would be toxic for the fish and they wouldn't last long.

Maybe one of our members has a hand held TDS meter that they could dip into a new batch of salt water and let us know what the TDS reading is.

 

This is correct +1

 

0 TDS is normal for new filters. Change filters when they're about 10% of your tap TDS.. Or sooner if you want.

 

Only industrial TDS equipment can measure saltwater. Our hobbyist equipment would just go "off the charts".

 

Yeah, I've done it before.. can't get a reading.