Substrate, pH, and water changes - The Planted Tank Forum
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post #1 of 7 (permalink) Old 08-21-2012, 03:50 PM Thread Starter
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Question Substrate, pH, and water changes

Dumb noob question:

My tap water pH is 7.6

If I set up a tank using a substrate that lowers pH, like Amazonia ... Won't water changes be a problem for the fauna? If I do a 20-40% water change I'd expect a huge spike in pH.

Would I need to mix water to match the pH before it goes in?
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post #2 of 7 (permalink) Old 08-21-2012, 04:40 PM
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Huge water changes with a high pH, high gH water will wear it out faster. Depending on what you are keeping in it, fish may not mind the change. Shrimp will though. Most who use buffering substrates use RO water with it, as RO even remineralized with a gH booster will still lack kH and therefore buffer down very easily by the soil and will minimize pH shifts.

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post #3 of 7 (permalink) Old 08-21-2012, 05:38 PM Thread Starter
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I won't set up my RO system again until I move. Would it be a mistake to adjust the pH of tap water to match the tank before using it for a water change?

Livestock will be 5x CPD, 5x boraras merah, 2 spotted blue eye, 2 amanos, 3 blueberry shrimp
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post #4 of 7 (permalink) Old 08-21-2012, 10:33 PM
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I have CPDs, Spotted Blue eyes, Corys, Ember Tetra and shrimp (blue velvet neos). My tap water is 8.4 PH until it degasses to 7.2. I do a 50% weekly water change and a few times (when I've forgotten that the siphon was running) larger changes of 70%. I've never noticed any issues. If you're concerned you could do more frequent smaller changes or let the water sit out with an air stone (I did this for months, filled a tub with water and an air stone and let it degass for several hours, then I tried it from the tap and as I said it's been fine).

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post #5 of 7 (permalink) Old 08-21-2012, 11:26 PM Thread Starter
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Thanks to both of you for the input.

So far my tap water and tank water have the same pH and it's very stable, but I'd like to switch from clown puke & plastic plants to something more attractive and plantable. I'm torn between eco-complete, which should leave my pH alone, and one of the ADA substrate systems.

For light I switched out the LEDs in my Fluval Edge 6g for a 27W sunlight CFL. I'm afraid I've gone from too little to too much light. After doing some reading I'm now concerned I need to reduce the lighting or deal with CO2 injection, which I really don't want to mess with in that little tank.

If it helps, I think the LEDs put out around 300lm and nearly all of it ends up in the tank. The fixture I chopped up and put into my Edge was rated at 1300lm and I guess maybe 70% of the light ends up in the tank.
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post #6 of 7 (permalink) Old 08-22-2012, 02:19 AM
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Fish (probably shrimp, too, but I am not sure) are not so picky about pH.
What makes the difference is the mineral and salt content of the water.
Fish regulate the amount of water, minerals and salts in their cells, and adapt to the level of these materials in the water. This is the Total Dissolved Solids.
If the TDS of the water changes, fish need to change the way they deal with the water/mineral/salt balance in their cells. Small changes are easy to adapt to, but larger changes take time. When the change is sudden (like a water change with the wrong water, or moving them to the wrong tank) the fish cannot adapt so fast, and they die.

If you have a tank and fish with a certain GH, KH and pH, and you do a water change that results in the TDS, GH or KH rising, you can make a change that is up to 15% higher, and the fish can adapt OK. It does not matter what the pH is doing, as long as it is anywhere within an acceptable range.

If your tank has harder water than the new water you can make a water change that results in 10% lower TDS, GH or KH and the fish will handle that just fine. Again, it does not matter what the pH is doing, so long as it is not widely out of the range the fish can handle.

For fish, the pH can rise suddenly or crash from CO2, and this is fine with the fish. If you alter the pH with salts, acids, buffers or similar materials you are adding to the TDS of the water, and the fish may not be able to handle that. It is not the pH, or the sudden change in pH, it is the changing levels of TDS.
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Set up a tank with ADA or similar product.
This substrate (and a few others) will remove the carbonates from the water.
Lower KH means the pH is more free to change. Other things in the water will alter the pH. 'other things' might be peat moss, Indian Almond Leaves, CO2, certain buffers like phosphate and products like pH Up and pH Down, and so on.
The tank adjusts, the fish adjust (the substrate removes the carbonates slow enough for the fish to adapt).

Then you want to do a water change, and the water has higher KH than the tank. Higher pH, too.
1) Test the TDS of tap and tank.
2) Test the GH of tap and tank. Sometimes the plants are removing enough calcium and magnesium to make some changes in the GH.
3) Add whatever you want to the new water to make the GH the same as in the tank, and add aquarium fertilizer.
4) Test the TDS again. If it is as much as 15% higher than the tank that is just fine. You could do a 100% water change, and the fish will be fine.
If the TDS is more than 15% higher, you will have to do the math to see how big a water change you could do.
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post #7 of 7 (permalink) Old 08-22-2012, 02:21 AM
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I've been wondering about this too. My tap water comes out at a pH of 8 and my tanks run between 7.2 and 7.4. When I used to do really large (40-50%) water changes on my community tank my green neons would turn white for a couple days. I might have lost a couple of them this way. I stopped doing large water changes entirely and I've never noticed this problem since.

I don't have room to let 20 gallons of water sit out and air off so is there anything that can be added to tap water to lower pH temporarily? That way it can be added straight from the tap to the tank without causing any crazy pH swings?
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