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I got hard well water. I thought my media was causing my high ph but after media test in vinegar its not that. I measured my tap water after aeration. Just like TCLynx said, it goes up. it was 7.6 out of the tap and after 2 hours of aeration it was 8.2 and peaked out a few hours later at 8.6. So everytime I top off my system the ph is pushed up. My ph in the system has been 8.2 but now is down to 8.0 by itself. My understanding is that the plants will eventually rebel on me and die because of the high ph.

My question is what are my long term solutions to this problem? Use rain water only? Osmosis filter?

As an experiment I have added some slices of oak to a buck of water to see if the tannin lower the ph, but that still sounds like a band-aid on a forever problem.


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Pre-treat your top up water with Muratic (also called hydrochloric) acid (HCL) to lower it's pH. This incidentally has the benefit of releasing plant usable Calcium (Ca2+) and the fish, it would seem, can only benefit from the chlorides (used to mitigate nitrite toxicity/brown blood disease). Don't confuse chlorine with chlorides, there is no way you will be adding any chlorine to your system by using HCL to treat your top up water.

Don't treat the system water itself directly with any acid or pH down product. You're better off pre-treating just the top up water in a separate container then adding that slowly so as not to shift your pH down by more than 0.2-0.4 points in a 24 hour period (your fish will appreciate that).

Or, use rain water or an RO filter.

Treating the top up water with acid is also a band aid and I don't really recommend it as the long term solution either (it would probably just mean too much calcium in your water which can cause other issues with potassium.)

I am trying to collect rain water since I live in a location that gets some rain so that I can alternate using potassium bicarbonate as my buffer with the rain water when needed and then if I need calcium carbonate, I'll just use some of my well water to top up.

If you are in a location without enough rain, then an RO filter is probably the only real solution.  And you can probably do the same thing I want to do with the alternation of RO water and potassium bicarbonate when needed and use some well water when calcium carbonate is needed.

Thanks TC. I was afraid of that :) No worries I will start collecting rain water again. I just need to make it through the summer. How long do I have before the the plants start dying off? Also TC mentioned that the systems will naturally lower the ph themselves, but I assume if we are topping it off with high ph water then it counteracts the systems tendency to lower the ph itself?

Why is it that systems lower the ph overtime themselves? Is that because the carbonate is absorbed?



The bio-filter bacteria will use up alkalinity (carbonates) in the process of converting ammonia into nitrates so the nitrification process does help lower pH.

I've run systems for years at a pH of 7.6.  Some plants do fine and others struggle more.  You may find you need to supplement with chelated iron more and potassium deficiency may be more of a problem because of the excess calcium but you will still be able to get the system cycled up and grow some plants.  Tomatoes and lettuce still seem to grow and watercress will thrive in the cool season.

Thanks again TCL. By the way I enjoyed your Aquaponics site, an inspiration.

I did a little expieriment this morning I cut about a 3" oak firewood into 1" slices on the chop saw. I threw about 6 of those into a 5 gallon bucket full of 8.2 water. After only 4 hours it was down to 7.2. So I think the tanin releasing from the oak ( heavy in tanin ) is lowering the ph pretty signifcantly. This might be a good way to buffer the ph down slowly without killing a bunch of fish.

Maybe just pitch two or three of those into the FT, which is a 350g system right now. What do you think?

I know there has been talk of using logs as a way to bring pH down.  What I don't know is if that will be good for the plants or not.  It isn't something I've really been able to test very well myself.

I put four of those 3" oak slices into my FT but since I added another grow bed today along with the water from the well, I haven't seen any ph changes today. Even after the slices of oak and the new water, I have steady ph of 8. I hope to see the ph slowly creep down over this week because of the oak added. I will post an update after the week is up.

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