it has been always 70 psi

0.01 ppm? You're worried about that? I wouldn't be. However, I would be checking TDS after RO membrane before DI resin. When is the last time you changed the DI resin? Did you have the system apart at all or did this problem start on its own? Does it normally drain down in the DI chamber when you shut it off and refill when you initially turn it on or does it always remain full?

I just changed the DI resin like 1 week ago, The problem just start yesterday, before it was find and I flush the membrane for 10 minutes the last time i used which was a week ago

It does normally drain down in the DI chamber half way and then refill when turn it on again.

Hmmm...mine does that too (draining DI chamber down partially) ever since I changed the DI resin. Before I changed the DI resin it didn't drain down. I refilled the DI cartridge that came with the system (AquaFX). I never did figure out what the problem was, and it has continued to happen ever since. I didn't pay attention very closely when I removed the cartridge since I didn't realize it is refillable I was going to toss it and use a different refillable cartridge. When I noticed the AquaFX one is refillable I refilled it, and put it back in. I thought that maybe I didn't put it back right or I dropped an o-ring or something, but I have no idea. It is almost like some of the water is somehow bypassing the filter. I really just don't get how it does it...I think it is sucking air in from the RO waste line when the system is shut off, but I haven't actually tested that theory. I can't think of any other way for air to get in there, and the water to get out. I also don't get any TDS so that doesn't make sense either. I sent photos and the same question to AquaFX and although they tried to help neither of us could figure out the problem. Since I get 0 TDS from it, I just ignore it.

The DI chamber in my BWI 75gpd 5 stage system has never filled up since day 1. I get 0 TDS out so I don't sweat it. Sometimes it gets about half full after I've opened one of the pre filter housings or if I've run just RO for drinking water for a while. Doesn't take long to almost empty out once I start running the DI again though. I've read a few posts here and elsewhere with similar info, some saying it's normal. No clue how it works, but like I said, TDS 0, why worry?

Maybe you could put a towel under it, slowly unscrew the cannister, until it fills and then retighten.

You don't really ever want to be running any of the canisters half full. It reduces the capacity of the resins/cartridges.

Check and tighten all your fittings.

I can understand it being a problem if your pre filter or carbon block filter housings are not filling completely, but the DI stage on most systems is generally a refillable cartridge and it has openings only at the top & bottom, that is, the water can only enter and exit at the bottom/top since the rest of the filter is a non permeable plastic casing. Therefore, as far as I can tell, there shouldn't be a need for the DI housing to be completely full of water for it to work correctly. As long as there's sufficient water going through the housing to enter one side of the DI case and exit the other, I don't see the need to have the entire housing completely full. Carbon blocks & poly pre filters allow the water to permeate along the entire length of the filter, so yes, those housings need to be full for best performance. I'm just thinking out loud here and could be very wrong, but as I mentioned, I get 0 TDS out of my system and my DI housing has never been full. The resin is slowly changing colour from bottom to top which would indicate that the water moves from the outside of the cartridge, into the bottom of the DI casing and out the top. Pretty sure all the other housings work the same way as far as which way the water travels... from the outside of the filter, then through the center top to the next housing.

Having said that, I also had a refillable carbon cartridge between my 1st stage poly pre filter and my solid carbon block filter. I've since replaced it with another poly pre filter. These pre filters are always completely full and the refillable carbon filter looks to be the same type of housing as the refillable DI cartridge, so not sure why one would be full and not the other. Maybe because there's higher pressure at the pre filter housings before the RO membrane. I reckon by the time the water gets to the final DI stage, there's not a whole lot of pressure left. The pre filters, RO membrane and waste line bleed off a pile of psi. Makes sense that the DI housing may not fill up since there's such a slow output after both the RO membrane and out of your DI line. There's no back pressure there until your auto shutoff on the DI line kicks in, if so equipped. Quite certain all my fittings are secure and water tight, otherwise there would be bubbling or water leaking out somewhere with just over 80 psi source pressure and 60 psi before the RO membrane.

so should i be worry if my TDS is 0.01? what level should i worry for TDS?

What kind of special TDS meter do you have that reads to two decimal points? Mine is only good down to 000, no decimal points, just a whole number. So the best reading I can get on the readout of my dual TDS meter is 000. Usually I get 001 out of the RO membrane and 000 out of the DI. My tap water TDS is somewhere above 210. So to answer your question, anything above 000 out of the DI either means it is close to being exhausted, or the TDS out of your RO membrane is abnormally high and there's something wrong there. As far as what TDS is level one should worry about, I don't know, depends on your system and what that TDS is. Salt, calcium etc. will all cause your TDS meter to register above 000, but that's good TDS. Without chemically testing your source water, or by getting a report from the city, there's no way to tell what that TDS coming out of your DI stage is. But since it's an unknown, best to sort out what the problem is.

Here's a link to your city's annual report:

http://www.calgary.ca/docgallery/bu/...report_web.pdf

Looks like your incoming TDS could be anywhere between 141 and 301. Just noticed you're running dual membranes, in which case your DI should last a long time and TDS out of the RO should be very low.