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Discussion Starter · #1 ·
I have to be honest for a period of time I had been very busy and wasnt giving my tank all the attention it deserved. But lately I noticed a ton of algae growth so I checked my RO/DI water and it was ~296 tds!!! I checked and my tap water is only ~146 tds and my tank was ~336 tds, that explains the algae explosion. So I ordered all new filters for my RO/DI unit, except the DI membrane.

I did a 25% water change on my tank and saw the tds down to 296 so I decided to check the water again. Water straight form the ro/di unit comes in around 001 tds but something is going on with my storage tanks (I use a 30g "Roughneck" for salt water and a 15g Rubbermaid for top off water) I tested the water in my 30g and it was 146 with some salt mix, after I mixed up a batch of salt water the tds went back up to 290 tds (Instant Ocean)?

Now the water in my top off container just keeps going up! it started off around 300, then went to 866 and after adding a few more gallons its now up to 998!! I tested the water again straight from the ro/di and it is 001. When I put the new filters in I ran a container full of water in this container and dumped it. I cant see anything in the container that would be causing this.

So what can I do, I cant use this water on my tanks? Is the tds going so high (296) normal with IO salt at about 1.022? What can I use to clean these containers that would be safe for the fish?
 

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there must be something wrong with your tds meter, the tds of seawater is around 36,000 mg/l. so what are the units this meter is showing when you say your tank is at 336? 336 what? mg/l (ppm), ppt (parts per thousand) or some other unit? typically a ro/di filter willl bring your water down to about roughly 5 mg/l (ppm). using a tds meter to determine if your ro/di unit is working is acceptable but not for determining the quality of your tank water. salinity is what you need to measure in your tank. if you don't have one i would get a good cheap refractometer from DIYReef.com or other on-line vendor or go to your lfs and get a cheap plastic hydrometer. also when was the last time you calibrated the tds meter, it should be done at least every 6 months or more.
 

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Discussion Starter · #4 ·
The TDS meter is an HM Digital that reads in PPM, no I haven't calibrated it in some time as I'm not sure how to do that? My readings using the ro/di and tap water are reading consistently, or seem to be at least.

It is definitely not the filters, as I posted water straight from the unit reads roughly 001ppm. Yes the membrane is a few years old but I don't think I need to change it yet.

I should have given some more detail in my first post since I lurk but rarely post. My current tank is a 100g w/2og sump that I have had running for over 4 years and before that I started with a 29g that I ran for about 1 year. It is basically a FOWLR but I have a few different variteis of mushroom in there currently. I'm not an expert, but not a newbie.

I was not using the TDS meter to gauge the overall water quality, I figured (possibly mistakenly) that since the water coming from the ro/di should be ~0ppm that the tank water should be close to that as well. I do have a nice refractometer for measuring my salinity levels and various test kits to measure nitrites, nitrates, ammonia, Ph, etc.

My major concern is that I am getting such ppm readings from my holding containers before the water ever enters the tank. A reading of 998ppm TDS in a 15g rubbermaid with nothing in there except ro/di water that measures 001ppm in a different container make me worry that there is something going on that could harm my fish. Is there a way to clean this container safely? Or should I just replace it with a new one? I assume that the reading in the container should be the same as whats coming out of the ro/di unit.

Also is a reading of 229ppm TDS normal for salt water mixed using Instant Ocean salt to a SG of 1.022 before it enters the tank based on reading 001ppm TDS at the outlet of the filter unit?
 

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If you go on HM's website http://www.tdsmeter.com/products/tds4tm.html you will see that their meters can only read up to 9990 ppm (mg/l). Like I said earlier your saltwater should read somewhere near 36,000 ppm (mg/l). So that meter definetely cannot do it, it is just giving you some random number instead of the true reading. If you have the salinity correct then you can pretty much assume that the TDS is correct in the tank so don't worry about it.

As far as the container is concerned it shouldn't leach any thing into the water but if you've ruled everything else out get a new one. Their cheap enough and test it with a small amount of RO/DI to see what you get.

To cailbrate the TDS meter you need to get a standard of a known TDS. HM's website says it factory calibrates it meters using a 342 ppm NaCl solution and you calibrate the meter by turning a screw. Standards are easy to find as most sites that sell these instruments also sell the standards. You should be calibrating it every few months at the least. pH meters on the other hand need to be calibrated daily just as a side note.
 

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Discussion Starter · #6 ·
Ok, so the TDS metere is really only useful for testing tap water or the condition of the ater coming out of the RO/DI unit then. You know what they say about using the right tool for the job....

I think I may just go out and get a new container, cheap insurance I guess.
 

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Yes the TDS meter is perfect for testing the water out of the RO/DI filter and will tell you when you need to get a new membrane or change out the DI. But it is basically useless for testing saltwater. Also with it not being calibrated in so long the problem with your storage water may all be caused by the meter not working. If you have problems with a new container then it is defintely teh meter. Get a standard and see if the meter reads it correctly, if not adjust it with the set screw, then re-read the water to see what the meter reads. One other thing, these meters all usually have metal probes that get dirty and corroded and just cleaning them off may help. I usually use Q-Tips to clean mine at work.
 

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Discussion Starter · #8 ·
I always try to "blow dry" the electrodes on mine after rinsing with fresh water. Although nto being calibrated in some time, my meter does give consistent readings on my tap water as well as the RO/DI water dispensed into a seperate container, even after testing the very high readins in the holsing container.

I agree that calibrating would be a good idea. Do you know where to get the "Standard" from? I looked on the website and checked a few distributors but no one seemed to list it seperately.
 

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Yeah, salt is a solid and it dissolves in water. Thats why it was reading so high. As for the unit, just calibrate it, they seem to go out of calibration easy.
 
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