plants lowering pH?

[norcalg]

Hello,
I've got a 55 and I upgraded the lighting (2x54w T5) and planted (moderately) 5 days ago. Since then, my pH has been steadily dropping, from a steady 8.0-8.2 a week ago to 7.8-8.0 the day after planting and down to 7.4 today. I haven't added any fertilizers or root tabs or anything. Ammonia and nitrItes have stayed at 0, nitrates have stayed at 10 ppm. I think the plants look happy but I'm not very plant-savvy. Not Dead = happy.

Is this a cause for concern or something I need to fiddle with or just a happy side-effect of planting? I'm not doing any CO2 (yet).

Also, I have a 10 gallon with 15W that I planted at the same time to try and deal with some steadily high nitrates. In that tank, the pH hasn't changed at all and the nitrates are still high, (20-40ppm today, no change from a week ago).

Thanks!
~g

 

[rich311k]

What is the substrate in the tank? What is the PH of your tap after standing out? Are you adding CO2? Any new driftwood in the tank?

 

[An t-iasg]

Rich has raised some very good questions, especially the one about your standing pH. You should always have a good idea of your baseline pH.

What plants did you add? If you upgraded your lighting, you maybe added some fast growers that use up the nutrients in your water.

A possibility - the plants may be using up the KH value of your tap water. It may be helpful to get a KH kit (some brands include a GH kit too) and test the KH value of your tap water. You can test for KH right after pouring the water from your tap. If the plants are using the KH present in the water to fill their carbonate needs (I hope I'm wording this correctly!) then you'll see your KH drop. A drop in KH will cause a drop in pH.

This drop in KH and pH happened in my tank. I noticed my pressurized CO2 was not turning on since the pH didn't get high enough to make the solenoid kick on. I added Seachem's Alkaline buffer to boost my KH and also raise the pH. Soon the pH was at a high enough level to turn my CO2 on. I have to add some Alkaline Buffer at every water change. I like the Seachem buffer since it corrects a known problem with my water (helping to buffer and increase my KH). Some other additives, like a pH Up product, should not be used since they have a tendency to "rebound". I see that you don't have CO2 and I wouldn't suggest adding a buffer arbitrarily unless you take readings of KH and pH several times to try to establish a pattern of what is going on in your tank. I just told my story so you could understand how KH and pH work together.

Another thing I thought of - when was your last water change? Water changes replenish the KH buffers naturally, provided your tap has at least a KH of 3. It is normal to see a slight drop in pH right before a water change. If that is the case I wouldn't worry too much (still try to get a baseline KH/pH of your tap water and tank water). As long as a water change brings the KH and pH back up to your usual levels, everything probably is fine.

 

[norcalg]

What is the substrate in the tank? What is the PH of your tap after standing out? Are you adding CO2? Any new driftwood in the tank?

Substrate is PFS (50 pounds) and Tahitian Moon Sand (20 pounds). pH of tap water (hose water, really to bypass the water softener) is 8.0-8.2 (between them, not varying from one to the other) after standing out. No CO2. No new driftwood. The wood that's there (3 pieces, 8-12" each) have been there for a couple weeks with no difference in pH.

Rich has raised some very good questions, especially the one about your standing pH. You should always have a good idea of your baseline pH.

What plants did you add? If you upgraded your lighting, you maybe added some fast growers that use up the nutrients in your water.

I've been aware of my pH as it's high (8.0-8.2) but haven't fiddled with it, except adding driftwood to the tank which didn't seem to make a difference.

I added:
ludwigia repens
anacharis
wisteria
hygrophilia corymbosa 'siamensis'
sunset hygrophilia
bacopa
some tall grass-like thing that I didn't write down the name of. :?

A possibility - the plants may be using up the KH value of your tap water. It may be helpful to get a KH kit (some brands include a GH kit too) and test the KH value of your tap water. You can test for KH right after pouring the water from your tap. If the plants are using the KH present in the water to fill their carbonate needs (I hope I'm wording this correctly!) then you'll see your KH drop. A drop in KH will cause a drop in pH.

Interesting. My KH was high - high enough that I decided not to worry about the high pH as it was expected to be stable. I want to say is was over 9dKH and I'll test it again later - both from the hose and in the tank.

This drop in KH and pH happened in my tank. I noticed my pressurized CO2 was not turning on since the pH didn't get high enough to make the solenoid kick on. I added Seachem's Alkaline buffer to boost my KH and also raise the pH. Soon the pH was at a high enough level to turn my CO2 on. I have to add some Alkaline Buffer at every water change. I like the Seachem buffer since it corrects a known problem with my water (helping to buffer and increase my KH). Some other additives, like a pH Up product, should not be used since they have a tendency to "rebound". I see that you don't have CO2 and I wouldn't suggest adding a buffer arbitrarily unless you take readings of KH and pH several times to try to establish a pattern of what is going on in your tank. I just told my story so you could understand how KH and pH work together.

Thank you. I'll take a look later and see if I can determine a pattern.

Another thing I thought of - when was your last water change? Water changes replenish the KH buffers naturally, provided your tap has at least a KH of 3. It is normal to see a slight drop in pH right before a water change. If that is the case I wouldn't worry too much (still try to get a baseline KH/pH of your tap water and tank water). As long as a water change brings the KH and pH back up to your usual levels, everything probably is fine.

Saturday, the same day I added the plants. The pH started decreasing the next day. I plan on another water change this Saturday and I'll keep track of the KH and pH in the meantime.

Thank you!
~g

 

[jsoong]

A possibility - the plants may be using up the KH value of your tap water. ...... If the plants are using the KH present in the water to fill their carbonate needs (I hope I'm wording this correctly!) then you'll see your KH drop. A drop in KH will cause a drop in pH. ....

I think you are refering to biogenic decalcification.
see: http://www.thekrib.com/Plants/CO2/decalcification.html

However, this will increases the pH, not decrease it .... Yes, the KH will drop in the process, but the byproduct is OH-, which will increase pH.

I am at a loss to explain the pH drop. Are the plants healthy? Dead plants rotting will drop the pH, but I would imagine that you would need substantial plant mass to see that.

You might get a clue by measuring the pH in midday (with the plants actively photosynthetizing) and a few hours after lights out. If there is a diurnal variation (increasing in light, dropping at night), then this may be a function fo CO2 depletion .... although in my tank the change is only 0.2 or so, not the amount you are seeing.

 

[norcalg]

A possibility - the plants may be using up the KH value of your tap water. ...... If the plants are using the KH present in the water to fill their carbonate needs (I hope I'm wording this correctly!) then you'll see your KH drop. A drop in KH will cause a drop in pH. ....

I think you are refering to biogenic decalcification.
see: http://www.thekrib.com/Plants/CO2/decalcification.html

However, this will increases the pH, not decrease it .... Yes, the KH will drop in the process, but the byproduct is OH-, which will increase pH.

I am at a loss to explain the pH drop. Are the plants healthy? Dead plants rotting will drop the pH, but I would imagine that you would need substantial plant mass to see that.

I'd say so. I've got a few soft leaves that should be pulled but for the most part, healthy looking plants.

You might get a clue by measuring the pH in midday (with the plants actively photosynthetizing) and a few hours after lights out. If there is a diurnal variation (increasing in light, dropping at night), then this may be a function fo CO2 depletion .... although in my tank the change is only 0.2 or so, not the amount you are seeing.

I can do that. The pH reading from earlier (7.4) was taken after the lights had been on for a couple hours. I'll test again later tonight. I just tested the KH again and 9 dKH is still the reading. So it doesn't appear to have dropped any.

The fish seem happy, the plants seem happy. :? Well water, bah!

Thank you,
~g

 

[Zezmo]

Is the test and drop in Ph repeatable? That is, do you get the same effect after your next water change? If you perform the test an hour after the first reading, do you get the same reading a second time? Just a couple things to look at.

9dKh and 7.4Ph = 11ppm of CO2, this seems high for a non-CO2 injected tank. If the Ph is droping and the Kh is staying the same, this is generally indicative of CO2 changes. Which is unlikely in a non-CO2 injected tank. This leads me to think of testing accuracy as a likely culprit.

 

[NoSvOrAx]

My 20L planted drops over 1.0 in ph everyday. Twice a day I have to dump mad amounts of calcium carbonate into the water to keep it up. I don't have this problem in any of my other tanks. I'm pretty sure the Alt. Redneckii and the red ramshorn snails are the cause.

 

[jsoong]

9dKh and 7.4Ph = 11ppm of CO2, this seems high for a non-CO2 injected tank. .

CO2 outgassing would increase the pH ... If the CO2 is truly 11ppm out of the well, then after outgassing, the pH should rise to 8.

An alternative explanation of the KH/pH reading is a 2nd buffer present in the water, which would invalidate the kH/pH/CO2 calculations. Most common 2nd buffer would be PO4 from argricultural runoff. PO4 would tend to lower the pH. Lots of plants using up the PO4 could change the pH .... but again this would tend to increase the pH... not what was observed.

I supposed there may be a some other buffer that is increasing the pH, which when removed by plants, will cause a pH drop .... I have no idea what that may be tho ...

 

[norcalg]

Is the test and drop in Ph repeatable? That is, do you get the same effect after your next water change? If you perform the test an hour after the first reading, do you get the same reading a second time? Just a couple things to look at.

9dKh and 7.4Ph = 11ppm of CO2, this seems high for a non-CO2 injected tank. If the Ph is droping and the Kh is staying the same, this is generally indicative of CO2 changes. Which is unlikely in a non-CO2 injected tank. This leads me to think of testing accuracy as a likely culprit.

Uh, yeah. At this point, I'm willing to say testing accuracy was lacking.
Day before yesterday:
tap water:
9 dKH
pH 8.0

tank water:
10 dKH
pH 7.6-7.8

Yesterday:
tap water: (after sitting out 18 hours)
8 dKH
pH 8.0

tank water: (after lights had been off overnight)
8 dKH
pH 7.6-7.8

And today:
tap water: (after 36+ hours)
9 dKH
pH 8.0

tank water: (lights had been on for 2 hours)
8 dKH
pH 7.8

I think the 7.4 pH tank reading was in error. I think that I am getting some small reduction in pH from the plants or the lights(?) but a) it's not precipitous and b) it's welcome. My fish are happy, in good color and continuing or beginning spawning behavior. The plants are growing and look healthy.

You might get a clue by measuring the pH in midday (with the plants actively photosynthetizing) and a few hours after lights out. If there is a diurnal variation (increasing in light, dropping at night), then this may be a function fo CO2 depletion .... although in my tank the change is only 0.2 or so, not the amount you are seeing.

That could be the case. I'm doing a PWC later today and I'll test after and again after lights out. This is almost as much fun as testing through my fishless cycle! Although, wow, I'm embarrassed by my less-than-accurate testing. My KH readings for the tap water should be the same every time, right?

Thanks for all the assistance,
~g