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DiscusLoverJeff
02-11-2012, 12:07 PM
Hello,

2 years ago I bought this RO unit;

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=190450639900

My question is this, when I purchased the 50gpd unit 2 years ago, I was getting a ph of 6.4. Then last year after I replaced the filters according to the 1 year cycle, my ph climbed a bit to 6.8. I upgraded the unit to a 150gpd last May (which for some reason I do not get) and the ph stayed at 6.8. Over the last 3 months, the ph has been above 7.4. Now, nothing changed except the output. I changed filters regularly.

Can anyone tell me why this is happening possibly? My tap water ph has not changed, it's still 7.4/7.5. After installling the new filters and running 5 gallons through the system today, my ph is still over 7.4.

When I upgraded the unit to 150gpd I was averaging maybe 100gpd ( I am sure water pressure changes the outcome) after changing the membrane and flow restrictor. But that should not effect the ph.

Thank you,

Jeff

discussmith
02-11-2012, 12:44 PM
You haven't said if you checked the tds of the water ever. If your original unit performed in the let's just say 99%+ rate meaning very little tds made it through the membrane and your new membranes function in the say 95% or < range you will still have some hardness in the product water effecting PH. This of course is mere speculation. Pressure and temp. also effect the membranes effectiveness and these may have changed since the beginning also. You must understand also that even though you read a PH over 7 that the buffering ability of your product water could be extremely weak and just a slight amount of acid could cause that PH to crash. This means that the normal bio functions of your fish can cause that PH to change rapidly. When I used R.O. water my Ph started at 8.8 to 9 and came out at 6.8 to 7.2 but the tank water was always at 6.0 to 6.5. The TDS generally ran from 320 to 350 ppm before and was 4 to 6 ppm after.

DiscusLoverJeff
02-11-2012, 12:50 PM
Sorry, my TDS is always checked weekly and it was in the range of 2 to 3 when new. After one year, it went up to 4 to 7. Before changing the filters I noticed the last few weeks it climbed up to 22.

With that said, I tested it now after running the first 10 gallons off the new filters (keep in mind the membrane is only 8 months old) and the TDS is 32. Whats going on? I have 2 TDS meters and they both read the same.

kent1963
02-11-2012, 01:57 PM
My guess is the rejection rate on the new membrane is 90% I know the filmtec 100 gpd are.The lower gpd units are 98%.

Discus Origins
02-11-2012, 04:12 PM
Jeff sounds like the new membrane is not as efficient as the last one. I have a 150gpd unit that outputs at TDS of 6 before going into DI. Have to be careful what replacement membrane you get, have to look for TFC membrane with rejection rate of 96-98%. Most of the commercial membranes are only at 90%.

JamesHe
02-11-2012, 05:52 PM
pH of RO is not important, it could effect by CO2 and with low dissolved solids, pH could swing big either direction.

DiscusLoverJeff
02-13-2012, 08:52 PM
Thanks Mark,

The TDS after a day of new filters is still 32. I know its not a problem because I mix with a bit of tap or RO Right to get it stable for my planted tank and pairs. I do mix 80/20 RO/Tap for the F1's. So TDS for them is about 170/180.