Water quality ?

[rtenzo02]

I've been researching and have not been able find a answer to my question. Hopefully someone can clarify things for me. I compared water perimeters taken from a couple major colleges on sea water, and it appears the TDS level is between 30,000-50,000 PPM. My tap water has 229 MG/L which is MUCH less than natural sea water. Ive read online that TDS is a huge problem for saltwater tanks , if that is so, why does natural seawater have a very large amount of TDS ? With the unit of measure, the size of the ocean vs the size of lets say a 75. Gallon tank should not matter. Also chlorine is found in sea water in the form of sodium chloride, and i beleive it makes up around 50% of the waters chemistry. The city I live in also if I am correct uses chlorine in the form of sodium hypochlorite which doesn't contain hydrogen as sodium chloride found in sea water , both are cleaning agents. With that said, why are ro/di systems so important for saltwater tanks ?

[shifty51008]

you really can't measure water quality of SW with a TDS meter, you will need to run independant tests to determine quality. TDS meters just say how much total disolved solids are in the water not what the each of the solids are.

when starting out you want to use RODI water that has 0 TDS and a quality salt mix, this is to alow you to know whats in the tank, using tap water you can be adding copper, ammonia, diffrent metal's, ect. that can be harmful to fish,inverts, and corals.

[disc1]

TDS is a measure of total dissolved solids. Salt water has salt (a solid) dissolved in it. So yes, the TDS is very high. 35ppt saltwater corresponds to 35000 TDS.

Where you want zero TDS is the water coming out of your RODI. That should be clean and have absolutely nothing in it. Then you are going to add salt mix and bring it up to 35000ppm TDS.

TDS just tells you how much stuff is dissolved, but not what it is. So when it is salt mix you know it is safe stuff. The stuff that might be in the freshwater before you mix in the salt is another question. You don't know what that is and it might well be detrimental.


As for the other question, there is a huge difference between chlorine, chloride, and hypochlorite. Both chlorine and hypochlorite are powerful oxidizers. They will eventually become chloride once they've oxidized something, but it is that oxidizing action that destroys living tissue and kills your fish and corals.

Chloride is the fully reduced form of chlorine. Chloride doesn't have that oxidizing action, it has already used it up. It is indeed the most abundant ion in seawater.

[rtenzo02]

Great, with that said the copper level alone around here is .030 mg/l which is considerably higher than the .25 ppb found in sea water. That alone is enough to make me purchase a ro/di unit, and thanks for clearing that up ! Might have been stuck on the big picture when i could have broken it down ! Thanks again !

[rtenzo02]

And thanks disc1 for clearing up the chlorine side of things !

[Twistofer]

Cities also use other organic chlorine compounds to "purify" water. These are easily removed with RODI units, but be sure you pass the water first through a carbon block before the water passes through the RO membrane.