RODI question

[nwsharksfan]

I have a marineland RODI unit that I've had for the better part of a decade that I just started using after a long period of sitting in the garage. After issues with algae I took a look at the RODI unit and saw a couple green flakes (algae?) in the first filter and the color changing resin looked pretty brown to me. I ordered a TDS meter and replacement filters (but not the membrane) for the RODI unit on the assumption that the algae problem was due to an ineffective RODI filter. Well, the TDS meter got here before the replacement filters. I tested the RODI water and it was 2 ppm. Is it safe to assume this means the filter is fine and I should store the replacement filters away for a while? Or play it safe and start fresh with new filters?

Since I have a new toy, I tested my tap water and it was 72 ppm. Filtered water from fridge was 68 ppm (really getting my money's worth from the fridge filter). Tested the water in my tank and it was 728 ppm. Just out of curiosity, is there any established range for what tank water should be?

 

[Delapool]

Curious on this myself, did you come across anything? I have KH and GH guides but nothing on TDS.

 

[ImACoolguy]

I don't know the exact range but 700+ in the tank seems quite high


Caleb

 

[hjsvt]

I run a small RO with no DI for all my aquarium water because we have super hard well water and the house water all goes through a softner. I've been using my RO about 8 months now and my ppm has risen to about 9. I can't remember what the well versus softner water numbers were at this point because it's been a while. So I would think your membrane is working well at 2 ppm. With DI you should be zero. So I would suggest replacing your DI resin. Also I read somewhere that your Carbon and Sediment cartridges should be changed every 6 months like clock work to maximize the longevity of your RO membrane.

At one point several months ago when I started the RO for freshwater journey I read somewhere that recommended aquarium TDS should be 400 or less. I would be a little concerned with 700+ especially if your tap water is only 70+ ppm. I won't recommend making any drastic changes though. A slow gradual shift down to a more reasonable number over several months is probably the best choice.

The third bullet down talks about the 400 or less in this link.

There are also good discussions about this on other forums but I don't want to inappropriately link anything here. I googled "recommended TDS range for freshwater aquarium" and got some great links.

I'm curious how old your aquarium is and what you are using to top off water levels. Have you heard of Old Tank Syndrome? Might also be worth googling and reading about that too. You do know about evaporation loss leaving the minerals to add up over time. This can also cause the TDS to rise.

Hope this helps and good luck.

BTW I keep my community 29 gal heavily planted between 250-325 and my 10 gal heavily planted shrimp tank between 200-250.

 

[J.Mcpeak]

Archived links. May be useful?

Total Solids (TSS and TDS) in the Freshwater Aquarium

[EnvirSci Inquiry] Lehigh River Watershed Explorations

 

[Delapool]

Just had a look at our tap water report out of interest and it is roughly 400 to 500 mg/L. Across the city it was 200 to 500 mg/L. From memory our suburb is a little high in sodium or chloride I think.

 

[nwsharksfan]

My FW tank is about 450 ppm. I mixed tap water with salt mix to a 1.024 specific gravity and the TDS was 700. Now, the tap water has a TDS of around 72 - so this would unscientifically make newly mixed salt water 628 TDS. Given the calcium supplements, manganese, and organic material in the tank 728 seems to be about right.

I'm sure my fw tank is little high because it's an Oscar tank. Those things get the tank all poopy before I can refill the tank after a water change.

My fw tank is 7 years old and I use tap water with prime. Don't see much point to using RODI water in a freshwater fish only tank.

 

[nwsharksfan]

... and I apologize for not making it clear that it was a sw tank that had the 729 TDS to begin with. Didn't occur to me that people would use RODI for freshwater.

 

[ImACoolguy]

... and I apologize for not making it clear that it was a sw tank that had the 729 TDS to begin with. Didn't occur to me that people would use RODI for freshwater.

That does make a difference lol. It's often used in tanks with more sensitive livestock or from tap water issues.


Caleb

 

[J.Mcpeak]

... and I apologize for not making it clear that it was a sw tank that had the 729 TDS to begin with. Didn't occur to me that people would use RODI for freshwater.

I'm pretty sure you mean 7290
Look at the end of the digit readout, a small symbol appears for x10.
(My puffer tank is 1.005 and is 3040 TDS)

I'm not sure you can have 1.024 and only 729 TDS using salt mix.

I use RO in all of my systems, because there are no unknown variables in home made water!
My TDS ranges from 086 for soft water to 116-124 for standard stuff.
Harder water is in excess of 200 (up to 300-350 or so)

 

[nwsharksfan]

Correct. 720 x10.