pH and a Tale of Two Tanks....

  • #1
This will be a little long. I want to be sure I cover all the bases to see if anyone can help me ID a root cause. I lost a baby Frontosa to dropsy & did my obligatory water test to make sure all was well. It wasn't.

Tank 1 Info:
  • Size: 55gal
  • Filter 1: Magnum 350 w/ sponge pre-filter, Seachem Matrix media, fluidized sand bed & UV sterilizer. Turns over 120gal/hr
  • Filter 2: Magnum 350 w/ filter sleeve & filter floss. Media canister alternates Purigen & activated charcoal. Turns over 280gal/hr
  • Bubbler: 12" Bubble wall powered by a tetra quiet 150
  • Substrate: Silica sand
  • Lighting: 2x T5 6700k
  • Weekly water changes of 30%-50% (along w/ Seachem Prime)
  • Tank has been up & running since January & is typically VERY stable

Parameters at TOD
Last water change was Friday. The above measurements were from yesterday. So the pH was less than 6.0?!?!? Followed up my chem strip test w/ TWO API kits. The pH really was around 6.

  1. Tested the cold tap water; it's 7.8 - 8.0
  2. Tested the hot tap water; same as the cold
  3. Thought about any new additions to the tank. I DID add some more sand saturday......
  4. Did a series of partial water changes throughout the day to slowly bring the pH back up; it's now 7.2.
  5. For grins, checked my hospital tank. It got a 90% water change on Friday. pH was also > 6.0!!!

Tank 2 Info:
  • Size: 10gal
  • Filter: Sponge pre-filter, HOB filled w/ Seachem Matrix & occasionally charcoal or Purigen
  • Bubbler: None
  • Substrate: Pea sized gravel
  • Lighting: Incandescent
  • Frequent water changes + Prime
  • Currently medicated w/ Flagyl
  • Tank is frequently taken down & scrubbed out after sick fish are finished healing. It is going through a mini-cycle.

Parameters at TOD
  • Ammonia = .02 ppm
  • Nitrite = Trace
  • Nitrate = Trace
  • pH = <6.0

As with the large tank, I did a series of water changes to slowly bring the pH up to 7.2.

So I have two COMPLETELY different tanks, both filled from the same tap & I have a pH problem in both! I got to thinking about things that ARE common between the two tanks:

  • water supply (tap w/ pH ~7.8-8.0)
  • water treatment (Seachem Prime)
  • fish keeper (me)
  • foods

what could possibly be going on here? a drop in pH that low only a few days after a water change w/ high pH water is pretty significant.

for grins, I tested one of my brine shrimp cubes to see if it had a significant effect on pH. one cube brought 12oz tap water from ~7.8 to ~7.3. that's significant, but the size of the water bodies (especially the big tank) should buffer this pretty easily. I don't use any other water additives other than what was mentioned above. foods have not changed & feeding quantity hasn't changed. stock hasn't changed recently.

I am stumped. what am I missing? any ideas are greatly appreciated.

  • #2
This might help:

(borrowed link from Ken)

  • #3
I would also recommend testing your KH value. I've added crushed coral to 3 of my 4 tanks to raise the alkalinity. They were not stable.

Links provided above are good ones. Especially the last one for properly testing the tap water.
  • Thread Starter
  • #4
thanks for the advice. thing is, the pH is usually stable in my big tank. it is puzzling to see it this far off, especially shortly following a sizeable water change. I'll try letting some water sit & bubble for a day & re-test.
  • #5
Did you add new driftwood or decor to the tanks? If it wasn't cured properly, driftwood could release enough tannic acid to mess with your tank's PH pretty significantly.
  • #6
Yah I'm kinda puzzled about this one too. Even if you did the PH test in a bucket.. Your PH should raise at the end if the true PH reading at the tap is incorrect. persay if there is too much Co2 in your water at the tap. Co2 dissolves in the bucket with the air stone and viola PH changes. Yet it would be opposite of what your having..not a drop.

I read that a well made UV sterilizer can indirectly lower the KH in a tank by affecting disssolved organic, which would indirectly affect your PH. Yet you only have it in one that rules that out.

I did read what Escapay was saying, read a few articles about crushed coral added to the substrate allowing for the buffers to keep the PH stable

Barring that, I've read that waste buildup in gravel and the filter if not thoroughly cleaned release acids during the breakdown that lower PH. I don't have the source for this, just something I remember reading and where I can't remember.
  • Thread Starter
  • #7
definitely has me stumped. in the 55gal, I did switch airstones from a little starfish to a bubble wall. I don't think that caused this. I do have driftwood in the 55gal, but it's been in there all year.

interesting note about the UV sterilizer; I will look into that. I rearranged the 55gal on Saturday, but I didn't add anything to the tank except the bubble wall.

I wonder if there was an issue with our municipal water or something? it's just such a substantial difference in such a short period of time, & the fact that the problem is identical in two TOTALLY different setups....

what effect does rotting food have on pH? i'm still relatively new to the hobby (a bit more than a year) & I struggle with how much i'm feeding. still, though, I haven't changed anything about my feeding habits in months. I clean out my canisters about every 4-6 weeks. the sand gets vacuumed weekly & the sand bed is stirred every two months to avoid buildup of nastiness.

headed home now; I will test & see where I am relative to yesterday's reading of 7.2 in both tanks.
  • Thread Starter
  • #8
big tank was 6.4 last night. I shut down the UV sterilizer. it usually runs 24/7. the water is already taking on a greenish tint. that's been my only form of algae control in that tank; that will be a new problem I'll need to solve. I have some tap water w/ an airstone sitting out. I'll check it this evening to get a 'true' pH reading on my tap water.

small tank back down to 6.0. still showing ammonia; I think part of the pH issue in that tank is that it's cycling. did a water change & will continue to do so every day until ammonia sticks at zero. once that happens, we'll see if the pH stabilizes.

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