Why water change day seems to grow aquatic plants better

Mar 20, 2013
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About the gas escaping from the plants, i.e. pearling, immediately during the water change, that's probably due to the lower gas concentration in the tap water. This forces the gas to be expelled from inside the plants where the concentration is high. I was able to prevent this from occurring by oxygenating the water with an air stone over night. So aside from the pH drop, oxygen was added to the water. No plants pearled during the water change. I infer that not only is my tap water extremely low in CO2, it is also very low in dissolved O2. Without an O2 meter, I can only infer that this is the case based on these observations.
 

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Solcielo lawrencia;119099 said:
After months of comparing frequent water changes (multiple times daily, daily, every other day, bi weekly) and weekly or twice monthly water changes, I see no improvement in growth with more frequent water changes. I notice no "bump" in growth as some have described. In fact, it's the opposite. If I do more water changes, plants seem to grow slower. If I don't do water changes, they appear to grow faster probably because I'm already adding CO2 and WCs reduce the amount. That may have to do with the water from the tap.

San Francisco tap water: out of the tap, pH=8.4. After passive degassing for 24 hours, it drops down to pH=7.4-7.6. Active agitation with an air stone drops it down to pH=7.2-7.4 in less than 10 hours. pH should climb as one would expect if the water were rich in CO2 and degasses, but that's not what occurs; pH drops. kH=2, so according the the pH/kH table, out of the tap, CO2 =0.2ppm. After air stone degassing, CO2 =3-4 ppm. There's more CO2 after degassing than there is out of the tap.

SF has issues with their alkalinity, not so bad right now. But come the rains, it'll change.
They struggle to maintain the Alk. Sacramento and American river water is similar. Same issues.

I get nicer growth after a water change. Water comes from the same sources. Exposure to air, fluffing the plant leaves and any algae or epiphytes off, reducing the organic loading, amplification of the bacteria via added O2. Tap will almost always have higher O2 than tank water.
It comes in that way(colder water holds much more O2) and is heated in a sealed vessel. Sometimes, rarely, that is not the case.
 

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Solcielo lawrencia;119124 said:
About the gas escaping from the plants, i.e. pearling, immediately during the water change, that's probably due to the lower gas concentration in the tap water. This forces the gas to be expelled from inside the plants where the concentration is high. I was able to prevent this from occurring by oxygenating the water with an air stone over night. So aside from the pH drop, oxygen was added to the water. No plants pearled during the water change. I infer that not only is my tap water extremely low in CO2, it is also very low in dissolved O2. Without an O2 meter, I can only infer that this is the case based on these observations.

If you take a sponge that's sogged good underwater, and then expose it to the air and then resubmerse, it'll pearl too.
Aquatic plants are mostly sponge like.

I'm suppose to send my O2 meter to someone, but if you want, you are in the SF area, I can loan it to you.
 

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Solcielo lawrencia;119124 said:
About the gas escaping from the plants, i.e. pearling, immediately during the water change, that's probably due to the lower gas concentration in the tap water. This forces the gas to be expelled from inside the plants where the concentration is high. I was able to prevent this from occurring by oxygenating the water with an air stone over night. So aside from the pH drop, oxygen was added to the water. No plants pearled during the water change. I infer that not only is my tap water extremely low in CO2, it is also very low in dissolved O2. Without an O2 meter, I can only infer that this is the case based on these observations.

If you take a sponge that's sogged good underwater, and then expose it to the air and then resubmerse, it'll pearl too.
Aquatic plants are mostly sponge like.

I'm suppose to send my O2 meter to someone, but if you want, you are in the SF area, I can loan it to you.
 
Mar 20, 2013
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Tom Barr;119135 said:
SF has issues with their alkalinity, not so bad right now. But come the rains, it'll change.
They struggle to maintain the Alk. Sacramento and American river water is similar. Same issues.
SF uses water from three different sources, but primarily from Hetch Hetchy, according to the utility company and sometimes they're mixed together. Sometimes I notice that there seems to be more gas bubbles in the water but that was the minority of the time during this past spring and summer when temps were hotter.

I'm suppose to send my O2 meter to someone, but if you want, you are in the SF area, I can loan it to you.
Thanks, I'd appreciate it! How much does one of those cost?
 

fishboyfromoz

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Back on auto water changes

So after reading this entire thread , I re-instated my diy auto water changer for 22% daily (over 20 min), just prior to lights on.
This is via an overflow, so the level in the tank does not change.

Will see how we go...
 

Matt F.

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Don't forget that there is a lot that happens between the water sources and your faucet (e.g. local pump stations, flushing, and soon to be UV filtration). Dechlorinator might also skew your o2 readings. Some things to be aware of.

Solcielo lawrencia;119158 said:
SF uses water from three different sources, but primarily from Hetch Hetchy, according to the utility company and sometimes they're mixed together. Sometimes I notice that there seems to be more gas bubbles in the water but that was the minority of the time during this past spring and summer when temps were hotter.


Thanks, I'd appreciate it! How much does one of those cost?
 
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gsjmia

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I thought it was the light getting brighter but I did WC with lights off and it still pearled.

Then, I saw the ET starting to pearl as I was draining the old water-then it occured to me:

Plants are under water pressure.
When you change water, you lower the water level reducing the water pressure.
Gasses from stems, roots, whatever, expand and migrate further out due to the lesser water pressure.
You fill the water back up, which increases the water pressure which squeezes the gasses out.

I guess the way to test this is with a continuous WC, i.e., refill at the same time as the draining is going on so that the water level doesn't drop.

If it still pearls, then its not the pressure.

I will try this next Sun.
 
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If that were true about pressure, then it should pearl when you add the water you just took out. It won't. I tried a few pages back in this thread.
 

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You can do the same thing with a sponge and submerged the sponge and then take it out, then resubmerge it etc, light is no longer a factor.

My take is since aquatic plants(pretty much universally) are "sponge" like, they take up the gases they are exposed to. Just like a sponge. So they have a sudden influx of O2 and CO2 and massive surface area for exchange when exposed to air.
Then we refill the tank back up, they are loaded with air(N2, mostly, O2 and CO2 etc), which can be used as a pulse of high concentration.

Excess gases are pearled off. So some is likely from Photosynthesis.

An EASY way to measure this?

Measure the O2 concentration before, during and after the water change.
Only plants and only the splitting of water will produce the O2.
Tap water will have a fair amount extra O2 once it is warmed up........but you can measure this incoming tap water and the tank's water, then subtract that from the build up for that day.

Test 1:
So say you do a water change 1 hour after the lights come on.
O2 is 7.05 ppm
The new water is 8.05 ppm O2.

Let's not have fish or other factors in here.
Do 100% water change.

Measure the O2 over the next 7 hours of light.

Test 2:
Repeat this the next day, but without any light.

Any difference in the O2 will be from O2 from the plants.



In reality, we do not do 100% water changes. You can compare the O2 readings without turning the lights off if you do the water changes later, say 3-4 hours later. O2 will degas fairly quick in my tanks.
Then see what the same O2 readings are on non water change days. You can also add a heater to a trash bin and allow the water to degas for 48 hours first at the same temp as the tank. Then use that and make sure it's 100% equal with the air.
Then measure the O2 on that day for the entire photoperiod and then the following day/s without the water changes.
 

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You can do the same thing with a sponge and submerged the sponge and then take it out, then resubmerge it etc, light is no longer a factor.

My take is since aquatic plants(pretty much universally) are "sponge" like, they take up the gases they are exposed to. Just like a sponge. So they have a sudden influx of O2 and CO2 and massive surface area for exchange when exposed to air.
Then we refill the tank back up, they are loaded with air(N2, mostly, O2 and CO2 etc), which can be used as a pulse of high concentration.

Excess gases are pearled off. So some is likely from Photosynthesis.

An EASY way to measure this?

Measure the O2 concentration before, during and after the water change.
Only plants and only the splitting of water will produce the O2.
Tap water will have a fair amount extra O2 once it is warmed up........but you can measure this incoming tap water and the tank's water, then subtract that from the build up for that day.

Test 1:
So say you do a water change 1 hour after the lights come on.
O2 is 7.05 ppm
The new water is 8.05 ppm O2.

Let's not have fish or other factors in here.
Do 100% water change.

Measure the O2 over the next 7 hours of light.

Test 2:
Repeat this the next day, but without any light.

Any difference in the O2 will be from O2 from the plants.



In reality, we do not do 100% water changes. You can compare the O2 readings without turning the lights off if you do the water changes later, say 3-4 hours later. O2 will degas fairly quick in my tanks.
Then see what the same O2 readings are on non water change days. You can also add a heater to a trash bin and allow the water to degas for 48 hours first at the same temp as the tank. Then use that and make sure it's 100% equal with the air.
Then measure the O2 on that day for the entire photoperiod and then the following day/s without the water changes.
 

fishboyfromoz

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Hmmm, so 7 days in with 22% change per day and big algal bloom (gda/bg)... Doh.
Two factors contributing - filter needed cleaning (done) and ferts were totally running out during the day (pearling stopped but when new ferts in > explosive pearling within 20 sec). Upped that a bit, was probably too lean given water changes.

Plants always seem to pearl strongly after water change, even though they are not exposed to air (new water in, overflows to drain).
 

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Today when I did the water changes, I decided to do them a little later and see how the plant's pearling response behaved.
They pearl far far more intensely 8 hours later than they ever have without the water change.

Next up, to measure the day of and the following day for O2 at the end high point of O2 concentration.
I did not do this today, but will next week sometime.

Now after 6-8 hours..........the new water's gas, temp, O2 effects etc, are degassed/equal. Thus all that pearling on the plants is from photosynthesis, not the sponge like leftovers or the tap water degassing etc.
The next day? The ferts are roughly the same still, CO2, lights etc. I can also measure the day before the water change for the Time @ =7 hours in to the light cycle.
Light is just starting to drop off from 100% at that time.

Seems if we have a higher peak at this time for the day of the water change vs the other 2 days on either side, this will be rather telling in terms of the water change effects.
This might help narrow down and rule out some possible causes.

Another thing to consider: how does plants tell if they are submersed or not? Hint: it involves a gas, not one we typically discuss on plant forums, but is well researched.
This gas may also have a positive effect on growth if it's suddenly removed.

Enzymes that are adapted to lower aqueous CO2 that are suddenly hit with a much higher rate from gas CO2, will also go into over drive. The extra O2 might be a lag response from the water change.
Nonetheless, I think there's strong observations that the water change does induce a higher rate of growth in the plants themselves.

O2 readings would confirm this.
 

Tom Barr

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Today when I did the water changes, I decided to do them a little later and see how the plant's pearling response behaved.
They pearl far far more intensely 8 hours later than they ever have without the water change.

Next up, to measure the day of and the following day for O2 at the end high point of O2 concentration.
I did not do this today, but will next week sometime.

Now after 6-8 hours..........the new water's gas, temp, O2 effects etc, are degassed/equal. Thus all that pearling on the plants is from photosynthesis, not the sponge like leftovers or the tap water degassing etc.
The next day? The ferts are roughly the same still, CO2, lights etc. I can also measure the day before the water change for the Time @ =7 hours in to the light cycle.
Light is just starting to drop off from 100% at that time.

Seems if we have a higher peak at this time for the day of the water change vs the other 2 days on either side, this will be rather telling in terms of the water change effects.
This might help narrow down and rule out some possible causes.

Another thing to consider: how does plants tell if they are submersed or not? Hint: it involves a gas, not one we typically discuss on plant forums, but is well researched.
This gas may also have a positive effect on growth if it's suddenly removed.

Enzymes that are adapted to lower aqueous CO2 that are suddenly hit with a much higher rate from gas CO2, will also go into over drive. The extra O2 might be a lag response from the water change.
Nonetheless, I think there's strong observations that the water change does induce a higher rate of growth in the plants themselves.

O2 readings would confirm this.
 

Tom Barr

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fishboyfromoz;119373 said:

These gases form HNO3 and H2SO4 when they come into contact with water vapor.
They quickly react with bicarbonate in water long before they make any contact with biological tissues.

They are serious human and plant health issue in urban and near coal and any other sulfur or N burning sources.
You have this vapor of strong acid microdroplets which come into contact with your lung tissues and skin, eyes etc.

Air pollution is serious.


Plants also have serious issues with it for the same reason.

Air does not have bicarb or other buffering abilities, so.......

Why do you think the coal swamps from 100's of millions of years ago are loaded with sulfur?
You can see the yellow sulfur if you pick up a piece of coal.
H2S formation...........
When that is burned, you get SO2.........add some water, now you have a strong acid.

Nasty stuff.

Coal energy is nasty stuff. They add Sulfur scrubbers, but.........they never use to and whined about it for decades and still do.
Smog like this killed many people in London not that long ago(1952 and killed about 12,000 people).
http://en.wikipedia.org/wiki/Great_Smog

Water is a bit different.
 

Tug

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With each water change we dilute the concentration of already dissolved waste and organic compounds.
 

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Tug;121779 said:
With each water change we dilute the concentration of already dissolved waste and organic compounds.

I think the link someone sent from Jeffery Funk was closer to the issue and also suggest why there's less algae in tanks with frequent water changes.
By adding less O2 demand in the tank(water changes do this pretty well), adding more O2............ the bacteria and micro inverts have more time to process and cycle the organic matter.
Algae are reduced, plants perk up(clean well cycled stable system), much like a Tropical rainforest where the soil is poor, but well and rapidly cycled. If you remove the recyclers or do not provide enough O2, or over load with too much organic matter(loading rate is the key there, not organic matter per se)
Types of organic matter make a big difference also.

If you over load the tank with fish progressively adding more and more, algae. It's a mess.
If you add peat or driftwood which leach tannins, not so much.
Driftwood that's been soaked a long time already has been "mineralized", much like soil.
And speaking of soil........ this is why folks should do frequent water changes(3x a week or so 50% each time) until the tank is well cycled, typically for 1-2 months, ADA AS or mineralized soil(or unmineralized if you want to do the water changes instead)
Such tanks or some even do daily, rarely have issues.

Also buffers against CO2 issues.
 

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Tug;121779 said:
With each water change we dilute the concentration of already dissolved waste and organic compounds.

I think the link someone sent from Jeffery Funk was closer to the issue and also suggest why there's less algae in tanks with frequent water changes.
By adding less O2 demand in the tank(water changes do this pretty well), adding more O2............ the bacteria and micro inverts have more time to process and cycle the organic matter.
Algae are reduced, plants perk up(clean well cycled stable system), much like a Tropical rainforest where the soil is poor, but well and rapidly cycled. If you remove the recyclers or do not provide enough O2, or over load with too much organic matter(loading rate is the key there, not organic matter per se)
Types of organic matter make a big difference also.

If you over load the tank with fish progressively adding more and more, algae. It's a mess.
If you add peat or driftwood which leach tannins, not so much.
Driftwood that's been soaked a long time already has been "mineralized", much like soil.
And speaking of soil........ this is why folks should do frequent water changes(3x a week or so 50% each time) until the tank is well cycled, typically for 1-2 months, ADA AS or mineralized soil(or unmineralized if you want to do the water changes instead)
Such tanks or some even do daily, rarely have issues.

Also buffers against CO2 issues.