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
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
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.