Question About Creating Soft Acidic Water - The Planted Tank Forum
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post #1 of 4 (permalink) Old 09-06-2014, 10:40 AM Thread Starter
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Question About Creating Soft Acidic Water

Hi All,
I'll apologize from the start that my post is going to jump all over and ramble a bit!!

I've kept (usually successfully!) aquariums for a good 25ish years now. I've always subscribed to the theory of letting aquarium fish adapt to the water out of the tap wherever I've lived in order to keep it simple. I've bread numerous fish and generally had very healthy tanks. I'm in the military and have moved a lot, hands down, the vast majority of places that I've lived have had very hard water in the 8.2+ range. I usually haven't had any trouble with most of the common fish we all see in big box stores, etc. (in other words, most livebearers, African Cichlids, even tetras/barbs). I've always been fanatical about regular maintenance, water changes, etc. and I know that stabilization is usually the bigger factor as opposed to a spot-on particular hardness or pH.

There have been fish that I've wanted to keep over the years (Discus, to name one) that have reputations as being difficult and/or not for beginners. In particular, I'm in love with the annual species of Killifish and am just itching to get involved in some of the various aquarium club breeder programs that are out there.

So, all of that was a build-up to my question! How does one go about achieving softer/more acidic water that is STABLE? Emphasis on the stable part! haha

I've been planning out my big dream fishroom (I'm getting close to military retirement now) and I want to focus on breeding and caring for some of the more specialized species of fish.

What I can't wrap my head around is the stability of RO water. As I understand it, after reading MANY articles here and in other places, is that running my water through an RO system lowers/removes the TDS and impurities in the water, effectively making it pure, but not necessarily lowering the pH. By making the water pure and removing buffers, isn't it much more prone to pH swings? I'm trying to learn/understand the steps to produce soft and pure water for fish that is ideal for breeding but also as stable as possible. Preferably without adding constant chemicals (aside from maybe extracts or essential minerals) or opening myself up to a disastrous water chemical situation. I've read about adding peat, almond leaves, etc., to affect water quality but this all sounds like black magic where the results may vary and fluctuate. In my mind that fluctuation sounds like a recipe for disaster. So, what do all the water guru's out there do?

Thanks in advance for any info or thoughts you might have.
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post #2 of 4 (permalink) Old 09-06-2014, 12:12 PM
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Softness and pH are two different things. GH is the total calcium and magnesium, whereas pH is how acid or alkaline the water is. KH is carbonate hardness, which is your buffer against pH swings. That's the variable that influences pH stability. Your description of RO is correct - it will reduce TDS and GH. I believe it also reduces KH but not totally sure. What you can do is mix water from your tap with RO to soften it. If getting to your preferred softness level also takes out too much KH, you could add that back with some baking soda. The more KH you have the more it takes to change the pH. For lower pH you can add CO2 (useful for a planted tank). Adding some peat to a filter would also lower the pH somewhat.

If you are getting discus, I would check with suppliers you plan to buy from to see what their water parameters are. Those bred in tanks tend to be more tolerant of harder water and higher pH than those caught in the wild. Its possible you don't have to do too much to your water.
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post #3 of 4 (permalink) Old 09-06-2014, 03:57 PM
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Hi, this is a bit 'messy' to read, but may be of help if you like lots of info ( as well as very clear answer above! There is a formula you can use to mix RO with tap water to get your desired GH (for fish) and then balance KH from there by mineralizing. If you keep the KH steady, I understand it helps keep pH stable.

I did test RO water but don't recall the pH. I tested the water from my chloramine/carbon filter system and my pH dropped from 8.4 to 7.4; KH also dropped.
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post #4 of 4 (permalink) Old 09-07-2014, 04:51 AM
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You are right. RO has no carbonates, so the pH is able to change according to something else in the water.

So you control the 'something else' so it is stable, and your RO water is stable.

Generally you will be adding a low level of minerals, including carbonate or bicarbonate to the RO water so that it will be the same every time you do a water change. That is stable.

I have several tanks with a substrate that removes the KH from the water. Then the pH drops. And stays there, until I add baking soda or potassium bicarbonate.
That is stable. 0dKH, pH about 6.0. It does not change by itself. I can do small water changes and the net change in pH and TDS is small enough that the fish are OK with it. That is stable.

Stable does not mean 'never changes'.
Stable means that any changes are small, and within the tolerance levels of the fish. Minor swings up and down.
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