pH Drop (!?) - Tropical Fish Keeping - Aquarium fish care and resources
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post #1 of 5 Old 05-23-2012, 12:54 PM Thread Starter
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pH Drop (!?)

Good Afternoon, Everyone.

I posted a few weeks ago regarding my 20 gallon tall. Since then I've removed all of the plastic decorations and replaced them with live plants (except the artificial wood in the center). The fish adore the new plants, the tank looks fantastic, and I've never been prouder.

However, there's been an issue I have a hard time figuring out the cause of. We change 25% of the water per week. We have a Mardel pH and Ammonia kit attached to the inside of the tank that shows us in 'real time' what our pH and Ammonia is. When the Ammonia goes up we make sure we change enough water to lower it to a safe and healthy level. Each week (regardless) we change, at least, 25% of the water in the tank. When we do this the pH bottoms out within 12 hours. The last time I stabilized the tank by changing small amounts daily until the pH reached 6.5, however the ammonia rose and we were forced to change the water 25% (per week) as usual. Once I stabilize the pH it is time for a water change and it bottoms out yet again.

Is it possible that I have too many plants per fish ratio? Everything I've read said that no, that is impossible.

  • 1 Dwarf Gourami
  • 1 Silver Lyretail Molly
  • 1 Dalmation Lyretail Molly
  • 2 Golden Panda Lyretail Mollies
  • 1 Emerald Cory
  • 1 Julii Cory
  • 1 Albino Cory

  • Wisteria (throughout the tank)
  • Spears (three total, two on each side and a marble by the filter)
  • Grasses (two in front)
  • Cabomba (all around rear and sides - just replaced a few pieces in the front right which isn't shown in the picture)

When we tested the tank late last week the pH was 6.5/7.0 and once we changed the water on Sunday the pH bottomed out at 5 (didn't register on the test strip) come Monday evening.

The local pet store suggested small daily water changes and pH up (only a few drops) after each water change to slowly (very slowly) stabilize the water.

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post #2 of 5 Old 05-23-2012, 01:04 PM
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You read correctly that plants will not affect your pH. You really can not have too many plants ;)

Is this a brand new tank? In a cycled tank, you should never, ever see Ammonia. I will say though that those stick on wheel things are horribly inaccurate, and do not last very long. The same is said of strips. Liquid tests are the gold standard for most people.

Have you had your GH and KH tested? Pet store should be able to do that for you. Your water utility might even give it in the water quality report. If your KH is really low, it's expected that your pH will drop over time. With a lot of soft water fish, this isn't an issue. A pH of 7, in most cases, is not ideal.
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post #3 of 5 Old 05-23-2012, 02:17 PM Thread Starter
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Originally Posted by Geomancer View Post
I will say though that those stick on wheel things are horribly inaccurate, and do not last very long.
I'm starting to realize that you are correct. It was rather neat when we first put it in, but after a few days the reading never changed, however it did respond when we did our water change and displayed low pH lvls. I'll look into a liquid test kit instead.

I'm glad to hear that I cannot have too many plants! I've really enjoyed incorporating them into my tank and find them to be incredibly beautiful.

The tank has been populated for about three weeks, with the plants being introduced two weeks ago. We had a some white stringy algae appear shortly after we introduced the plants and yesterday after I trimmed and replanted a few of the plants after the water change on Sunday. We were told it was 'normal.' The light is on for 8-10 hours a night, is this too much and can this affect water pH?
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post #4 of 5 Old 05-23-2012, 02:27 PM
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8-10 hours a day for lights is pretty normal. I do about 8 hours, anything more and I start to get algae. A timer works wonders for making sure you have a consistant light schedule, they are less than $10 in department/hardware stores. Light duration can not affect pH (that I know of).

Byron has writen a nice article about how GH, KH, and pH are related, so instead of repeating it I'll just give you the link:

Bassicaly we need to know the pH, GH, and KH of your source water and we can go from there.
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post #5 of 5 Old 05-23-2012, 05:56 PM
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Geo has mentioned it, but it is very important to know the GH, KH and pH of your source water, presumably tap water. The article Geo linked explains why.

Under no conditions use chemical pH adjusters, with fish in the tank. These can cause a fluctuating pH and this is far worse than a steady pH even if outside the fish's preference, though that has issues too.

When we know the numbers for the tap water [you can get these from your water supply people, they may have a website] we can somewhat forecast the pH. As you have mollies, the pH must be above 7, and the GH must be medium hard to hard. The other mentioned fish, though technically soft water, will manage provided the hardness is not too extreme.


Byron Hosking, BMus, MA
Vancouver, BC, Canada

The aquarist is one who must learn the ways of the biologist, the chemist, and the veterinarian. [unknown source]

Something we all need to remember: The fish you've acquired was quite happy not being owned by you, minding its own business. If you’re going to take it under your wing then you’re responsible for it. Every aspect of its life is under your control, from water quality and temperature to swimming space. [Nathan Hill in PFK]
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