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Can Nitrate filter increase PH?

Waterkeeper

Seedling
Joined
15 Jul 2015
Messages
1
Hi - Newbie to this forum, I am puzzled by a water filter I installed at home and which is causing issues with a huge PH rise. Sorry for the background saga, but is important - any chemistry guru's view would be massively appreciated. Another forum could not help so far.

Tank:
60L Freshwater, pretty heavily planted with low light plants, 1 Mopani wood, 2 Cories, 10 Chili Rasboras, 4 Guppies. Soon 3 Endlers to be added. No CO2, 23C, using Prime as conditioner (and Purigen), Fluval 206 Filter, no carbon, inert sand substrate. Tank running with mostly Seachem Matrix (and some of the Fluval things, forgot name) for 2 years. Water changes - see below, currently ca. 20% twice weekly.

Story:
My tap water is very high in nitrates (SE England, and has around 14dH KH and GH, and around 40 nitrates) PH out of tap varies, but is around the 7.8 mark. After many battles with RO water and bottled water, I came across a plumbed in system [not sure I can/should mention manufacturer?], which offered a Twin system of nitrate reduction and a general filter (metals, chlorine etc., bit like a Brita or such). Fits under sink. Fitted this, Nitrates came out close to 0, PH very low (some 6-ish), KH and GH were reduced to around 5. Tested Ammonia by chance, and had about 4 ppm (API test kit) of Ammonia. Could be Ammonium, I cannot distinguish. Long conversations with the filter provider, Southern water - just to find out if they knew the reason so I could correct it, as the Nitrate problem was finally solved. Tap water no ammonia/um, and when this filtered water was run through a Brita filter, the ammonia/um was virtually nil. No results.
The nitrate-reduction cartridge looks very much like Purigen, i.e. beige little beads - this is just my observation, the manufacturer does not state what this cartridge component is.

I then decided, as I had the 2 "canister" things plumbed in, to use 2 of the Nitrate cartridges (ie remove the "general" one and replaced with another Nitrate one), and voila, no ammonium, and other values as above including the very low Nitrate level. Phew. Happy days. Small water changes with this mixture, tank doing great, Nitrates well under control, PH stable around 7.6.

About 2 months ago, some 4 months after the dual Nitrate filter was used, I tested tank water, which I had not done for some 5 weeks as everything was well, and PH was suddenly 8.2 (!! API test kit). Had a few fish deaths but could have been illness from new fish - I won't go into more detail here.
Tested Tap and Filtered Water:
1) water straight from tap comes out at 7.8 - 8, when left 24 hours settles on 7.6 - 7.8. So a bit higher than 6 months ago, but not massively different.

2) The filtered water comes out low (under 7.2), when left for 12 - 24 hours goes up to the current 8.2, and the KH and GH has risen from initial values to some 16dH (previously very low at ca. 4-5dh).

3) When this filtered water is run through an additional Brita filter, PH down to ca. 7.2, very low KH (under 3)

Question 1- why does pH rise so drastically over night when letting the water stand, is this high TDS? I.e. is there a build up in minerals etc in the tap filter material? I read up on the internet but so much info out there.

Question 2 - has anyone got experience with such tap water filters either producing Ammonia/um - and if so, any luck in resolving the issue? , And any experience with cartridges that exhaust and then push up the PH and KH and GH so much? I can only reason the filter cartridge is exhausted and built up stuff, and now releasing it? Could this be? [I will order new cartridges soon and have a look then].

Apologies for the long post but I wanted to give you as much info as I can.

Thank you very much!
 
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