Can't get PH down

[juddpuppy]

I have a 54 gallon corner tank using RO water. I have had tanks set up many times over the last 45 years including breeding many egg layers, but my water source was always surface water from reservoirs. I moved and now my water source is city wells with off the scale hardness and high PH. I have had my current tank set up for 2 years but had no fish for the last year because they kept dying for no apparent reason. Plants don't live either. A couple months ago I began using RO water which immediately fixed my water hardness problem. I bought a large piece of driftwood to assist to lower PH and 6 bunches of Jungle Val, because I read it was tolerant of my water conditions. It immediately disintegrated and shows no signs of life. I have natural gravel with a substrate made for planting with live plants under that. I use a Fluval canister filter and Marineland side filter and have an airstone or two with 2 LED lights to illuminate to the bottom of the tank. I am trying to get my PH low enough to have tetras. The PH was well over 8 and I have used API PH Down to get it to what looks like maybe 7.8. I am assuming this has been my problem keeping the fish alive long term. Some fish change color when I put them in my tank. A bristle nose plecostemus completely changed shades when introduced to my tank, seemed ok otherwise, lived a couple months and mysteriously died. An australian rainbow fish changed color so dramatically I didn't recognize It. Numerous fish may live a few weeks seeming ok and die with no outward sign of injury or disease. Any Ideas on 1, if this could be a PH issue or is there something else I'm not seeing that could be the cause of death, and 2, how can I get PH to lower in general to introduce tetras and eventually Discus (I have used an entire bottle of PH Down over a few weeks and it has only lowered slightly).

 

[libertybelle]

Ph down isn’t your solution. It leads to rapid swings that are way more dangerous than stable non ideal ph.

I hope this is an obvious question but how are you remineralizing the water? You mention RO but you’re not using it straight are you. What are your other tests showing (ammonia nitrite and nitrate, as well as kh / gh).

What kind of natural substrate?

What is the ph of the water before you add it to the tank vs the tank itself.

 

[juddpuppy]

Sounds Like I need to look at something in my tank now

What I read said I did not need to remineralize water unless I was Deionizing it, which I am not. I have 3 stage with no deionizer. I am putting it straight into my tank and it has immediately corrected my hard water. The water hardness was about 10 times off the scale before and now it is great. Ammonia, nitrate and nitrite all test great. I do not know the KH and do not know what GH is. Bottom gravel is natural gravel I got about 15-20 years ago from a previous tank I had set up for about 5 years with no issues. I just rinsed it and put in to this tank because I couldn't find natural at my local shops . And the substrate under that was something specially made to use in planted tanks. I don't remember what it is called. It is black and tiny like fine sand.

I just checked, The ph of the water before I put it in the tank is 6.4. Sounds like I need to look at something in my tank. I have only used the RO water for about 6 weeks now replacing about 4-5 gallons at a time a week or two apart, mostly replacing evaporated water.