Plants love it when I do a water change.

[PhishNeslo]

also, the amount of disolved gasses in the water is a function not only of pressure, but temperature as well. tap water comes out a little cooler than tank water, and when it warms up it lets go of the gas. that is why warm tap water often looks cloudy at first (the hot mixes with the cold and makes the gas come out), and why water releases a bunch of little bubbles right before it boils, and why fish cant live in boiled water after it cools down . . .

m.lemay wrote "As the gases dissipate and rise to the surface the tank water is still more saturated with gas than it normally would bebefore a water change. Higher gas concentrations in the water column means that the oxygen the plants produce won't dissolve in the water as readily since the tank is at or near saturation levels, therefore it just bubbles and rises out of the tank rather than get dissolved into the tank."

is it a fact, that if water were totally saturated with one gas, a different gas couldnt be disolved in it? that seems to make sense, but i seem to remember something about partial pressures of gasses that say that are somehow indepenent of each other.

phil

[GulfCoastAquarian]

I can't believe I've missed out on this discussion so far! We're actually talking about partial pressures of gases now! Let me break out my Chemistry book, oh wait.. I burned it after I passed my first year getting my Bachelor's Degree in Mechanical Engineering! haha

This is making more sense now. M. Lemay described it perfectly. Regardles of whether or not saturation levels of one gas affects another, if oxygen has reached supersaturation levels (high pressure, low temp) and is introduced into the aquarium where plants are releasing oxygen gas, that seems to be the answer to the pearling. I honestly thought it might have been CO2, but this makes a lot more sense.

This still leaves me intrigued with these potential "defense mechanisms" that plants might be capable of. It is fairly common to research these mechanisms in reefs when adding corals. You'd never add a stinging Elegance Coral within a few inches of a Hammerhead Coral. They would kill each other within weeks. But I wonder to what extent aquatic plants are capable of such a thing? Regardless, no matter how well balanced your ecosystem may be, regular water changes still seem to be mandatory.

[SNPiccolo5]

This is very interesting, I was looking through my physics book one day (to find the reading assignment on momentum) and I opened it from the wrong end. I have those removeable nylon-like book covers. Well, the heading I saw was "freezing and boiling at the same time". I was curious, so I read about it. I'll explain it like the book did.

Boiling- Is actually a cooling process. When the water heats up, it gets sooo hot that instead of having to react with air to change from liquid to gas, the hottest liquid water transforms into gas from underneath itself leaving the water, hence cooling it. The lower the pressure, the lower the boiling temperature. That is why water boils under 100 degrees C in higher elevations.

Freezing- Water cools down and transforms into a solid. Happens at 0 degress C. I think it is dependent upon pressure as well, since when water freezes it expands, so if the pressure was great enough, the freezing temperature would actually drop below 0 degrees C.

At the same time!- Put a pot of water in a vaccume and start to lower the pressure. As the pressure lowers, the water will start to boil, and since boiling is a cooling process, it will also start to cool. Keep reducing the pressure until the water has boiled to freezing temperature and the water will be boiling the freezing at the same time. The bubbles will be popping under a layer of frozen ice on top...

I asked my teacher if we would ever do that, but she said that we didn't have a vaccum, but I want to do that some day! I know it is sorda off topic, but I thought it was very interesting!

-Tim

[aquaphish]

I have read several messages that consider other gasses aree the contributing factor to pearling after a water change. What other gasses are found in water??? I don't know anything about water chemistry.

[PhishNeslo]

the other gasses would be the same ones that are in the air (about 78 percent nitrogen, 21 percent oxygen, and .003 percent co2, or something like that), only more of them, because tap water is under pressure. btw, do we know where the gasses diffused into the water from? when it is under pressure it isnt exposed to air.

phil

[lanstar]

I'm not 100% convinced that it is just due to a higher concentration of dissolved gasses due to the pressure in the public water lines.

Here's why: It happens when I do a partial water change using reconstituted RO water. The RO water sits in a plastic 55 gallon trash can, heated buy a heater with a power head submerged in it to circulate the water. The RO water is not under pressure and hasn't been for days and days (on average). I dip it out, 5 gallons at a time, and add some RO-Vital to reconstitute the water and raise the GH/KH to about 5-6 dH. Then I pour it in the tank.

The plants still pearl more for about a day after doing the 20% partial water change this way. Although, they don't do it as much as they do when I to a partial change using regular tap water.

Just something else to confuse the issue.

Tim

[PhishNeslo]

it sound like there is some nutrient in the replacement water that is lacking in the tank, and they plants get happy when you change the water . . . maybe phosphates . . . thats what i think . . . maybe nitrates or something too. i would say that you should be happy, and do smaller water changes more often :-)

also, how are you raising the hardness? maybe the stuff you use to raise it is something the plants can use (like some form of carbonate or something) more easily than the C that was already in your tank.

[aquaphish]

I have to disagree with the theory of pressure. I don't use tap water so the pressure thing is out of the question. I use bottled R/O water and sometime the bottles set around for several hours and I also get the pearling effects when I do a water change.

I just thing that when you are replacing the water what happens you are agitating the water when you are adding it to the tank and it releases the O2 much quicker and then forms bubbles that get traped on the plants.

Does anyone remember all of those little bubbles on the sides of the tank when you first set it up??? Most likely there were no plants and you didn't add any nutrients into the water. I really think its just the O2 stauration in the water adjusting.

Or maybe it's just a strange alien invasion thing going on!!!:aah:

[PhishNeslo]

then you are agreeing with the therory of pressure, i tink

[Steve Hampton]

There is not one and only one reason why plants will sometimes pearl after a water change. It happens because the plants are transporting more O2 than the tissues can hold and this results in O2 passing through the tissues to the outer leaf surfaces. If the water has reached it's O2 saturation level then pearling will start with it's associated "bubbling". What triggers this increase in photosynthesis efficiency depends on a variety of factors at the time of the water change. IOW's in some situation's the pearling would be from the addition of water with high levels of O2 (tap water under pressure), some situations are from water containing PO4 (phosphates), some situations are from the water containing higher CO2 levels, some situations are from water having one or more missing trace elements, etc.

Then of course you have situations like mine. Water changes never cause my plants to pearl...my plants begin to pearl within 60 minutes after the lights come on and pearl for the entire photoperiod. Why? I add lots of N-P-K, traces, and CO2, my O2 levels at the beginning of the photoperiod are sitting near 100% satuation still. Oh, and I keep pretty light fish loads.

If it takes a water change to incude pearling then something is missing...in most cases it's either CO2 or PO4.

Sometimes trying to find a single answer isn't possible. The challenge about planted tanks is the lack of absolutes. Truely, planted tanks are more of an art than they are a science.

[m.lemay]

Steve: Now thats the best explanation(s) I've seen. Makes a lot of sense.

I think that in most cases people were noticing that thier tanks pearled more after water changes, not that they didn't pearl at all.

Keeping a planted tank is part science, part art, and part green thumb.

[aquaphish]

I dont think it is from just water pressure from the tap water that causes the pearling effects. Based on this reason--- when I set up my tank I only had flourite and two pieces of driftwood in the tank. I filled my tank with R/O filtered bottled water that sat around for at least 3-4 hours. When I filled the tank with in a few hours I had a tank filled with small bubbles attached to the substrate and walls of the tank. I would think that by haveing the bottles standing for a couple of hours, there would not be any pressure in the water as if it just came from the tap. Maybe I am just not understanding what you mean by pressure. But I'll assume that your inferring that the pressure in the pipes the O2 some how gets compressed and when it is released into the tank the pressure is also diminished and the O2 is then released in a rapid rate causing the bubbling effect.
I think it is caused by O2 being drawn into the water from the atmosphere when you are pouring the water into the tank. Juyst likme the effect of a waterfall. If you see a waterfall from under the stream of falling water you will see an abundance of bubbles which I believe is caused by the water being saturated with O2 when it is being exposed to the atmosphere. Please comment on this.

[shalu]

aquaphish, I think in your case it is the temperature effect. Warmer temp in the tank lowers the amount of gas the water can dissolve. As the new water warms up after your water change, "outgassing" occurs. It does not just contain O2, it also has all kinds of other gases just like air.

[lanstar]

Originally posted by shalu
aquaphish, I think in your case it is the temperature effect. Warmer temp in the tank lowers the amount of gas the water can dissolve.

I think I remember that warmer water can hold more dissolved gasses, not less.

To previous posts:

Yes, my plants start pearling right after I turn the lights on and pearl all day too. (I use Duplaplant and Yamato Green/Green-N.) They just do it more for about a day after a 20% water change - whether reconstituted RO or tap.

No, no bubbles collect on the glass after the water change... the plants just pearl more.

I still lean toward there being some micro-nutrient in the "RO-Right"/tap water that gets depleted and is partially replaced with the water changes.

Whatever the cause, it's a good encouragement to do a good thing--- fairly frequent partial water changes.

Take care...

Tim

[shalu]

Originally posted by lanstar
I think I remember that warmer water can hold more dissolved gasses, not less.

Sorry Tim, you got it wrong:P That's the same reason fish have trouble breathing in summer in poorly aerated non-planted tanks. There is less dissolved O2 at high temp.