Lowering Ph

[elmo666]

Hi. My discus tank, fully planted, generally runs at ph 6.2-6.4. My r/o, once re-mineralized, comes out 6.9 to 7.1. Probably end of November I bought 80% phosphoric acid to match the ph. Recently I've had a sudden outbreak of bba and many of the leaves on my banana lilies and various swords have been rotting very quickly. Last night I tested everything looking for a possible cause, and the only parameter that's changed is phosphate, which is very high, 4/5ppm, I've never seen this in my tank before. Could the acid be causing this. Thanks

 

[the_lock_man]

Well, yes, phosphuric acid H3PO4 is hydrogen combined with the phosphate ion PO43-

 

[TwoTankAmin]

I use muriatic acid for this purpose. Nasty stuff, be careful. I use 50% ro/di mixed with my tap. I am doing altum angels, so I also want to stain the water. I also use catappas. alder cones and a bit of peat. I also use rooibos tea but that doesn't lower pH or soften water.
 
My Tap is 7.1 pH, 5 gh, 4 kh and TDS are 83 ppm. The ro/di is as much to get the the KH down to help hold the pH down. Initially the tank ran at 4.2. I was brought up to 6.0 over many months. I have recently moved it up again towards my tap pH but holding the TDS in the 60s ppm range.
 
I run a continuous 3 way monitor for pH, TDS and temp. to help me keep things under control
 
No matter whether I try to hold it at 4.2 or 6.0, it still drifts up over the course of a week. The problem with adding the things I mention is they also raise the TDS. My personal experience with this all has been to teach me that it is the TDS more than the pH that matters. That is the fish are better off at 60 tds and pH 7 than at pH 6.0 and TDS 100.
 
Now my tank is not planted. so I am not concerned with how things might affect them. But I have other planted tanks. My best recollection is that plants start to do less well as the pH moves under 6.5. And they do not do well with very low TDS either.
 
Finally, are the plants folks still promoting a targeted ratio of phosphate and nitrate? If so this might be at the root of your problem. the thing is, adding the acid raises TDS and so will nitrate.
 

 

[elmo666]

Thanks for your input. I've never looked into the estimated index approach too much. To be honest I'm at the point where I'm ready to strip the tank and have a complete rethink. I thoroughly enjoy putting in any amount of effort into creating a,stable, supportive environment for my fish. I've invested more in my current set up than ever before. The substrate alone, highly recommended btw, cost £120, aquagro nutra soil. Tbh not at all impressed with it. I run denitrate in an attempt to keep the levels below 20mg/ltr, a surface skimmer, uv, pressurized co2, inline diffuser, twin eheim pro 350's, two low level circulation pumps. I'm fully aware that equipment doesn't mean success, but believe me I put alot of effort into this tank as well. The discus spawn regularly, and up until recently the plants flourished. Maybe I'm guilty of trying too hard and thinking too much.......

 

[DrRob]

Yes TTA, they still seem to be recommending a good ratio.
 
Changing things may have upset the balance of things and the higher order plants have suffered. As TTA also moots, lower pH isn't so good for some plants, so there's a balance to be had in moving the pH slowly. HCl would work well, assuming you're careful with it and move things slowly, phosphoric acid would indeed raise the phosphate levels effectively. It's also worth remembering that the water in the tank and the remineralised water won't always match. The ecosystem you have will have natural acid sources, and the water you're making will mostly just have buffers, so it may be that the tank will level out at a different level, despite having a natural pH that is slightly higher.
 
I do agree that you're making things complicated by trying to do two things at once, both growing lush plants and trying to chemically adjust the parameters with denitrate filters and pH adjustments. I've often got problems with low nitrate levels in my planted sets, despite adding more, so wouldn't use denitrate filters as well as heavy plant growth. It sounds like you have the makings of a great tank, and with some fast growing stems and a proper fertilise regime to get them flourishing you should be able to get rid of the extra filter gubbins and have a really nice set up.
 
As an aside, I'm also a minor fan of DIY remineralisation, if you really want to get into full control of your water, which would allow you to control the pH well.

 

[elmo666]

Thanks gentlemen. Dr. Rob, you have me intrigued regarding the remineralisation. I am indeed a very keen DIYer, I work as a maintenance technician, a qualified design and technology teacher, so tbh can turn my hands to most things, including any aspect of plumbing. As for my tank, well I'm now leaning towards stability and ease of regular, controlled water changes trying to marry the needs of the discus and plants side by side. I don't hold with the bare tank approach, love natural fauna, and the marriage of the two gives me a focal point that brings me great satisfaction. I'll send you a personal message to see if we can share ideas. Thanks