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post #1 of 12 (permalink) Old 03-29-2010, 02:00 AM Thread Starter
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Interesting observation

I've made the switch to using a python/50% water change routine instead of a 10% weekly WC with RO/DI water. I've made some changes to my tank over the last year based on what I've gleaned here from some people who really know how to do this but I was surprised by what I saw after I changed 50% of the water tonight: crazy, mad pearling from almost all my plants! Now, keep in mind that I removed 1/2 of the CO2 (was green with 4dKH distilled water DC) via the WC. Normally I have several plants that pearl all the time but not all and some of that could be due to the 3 power heads that I now use to circulate water but this was crazy! I mean some to the plants were smoking! I'm baffled as to the cause of this. Has anyone else ever seen this?


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post #2 of 12 (permalink) Old 03-29-2010, 02:53 AM
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Tap water is very highly oxygenated. Your plants are still producing the same amount of oxygen, but because there's already so much oxygen in the water, pearling occurs. They're not making oxygen any faster than they were before.

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post #3 of 12 (permalink) Old 03-29-2010, 10:48 AM Thread Starter
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Tap water is very highly oxygenated. Your plants are still producing the same amount of oxygen, but because there's already so much oxygen in the water, pearling occurs. They're not making oxygen any faster than they were before.
Sooo you're saying that the water is so saturated with oxygen that it can't hold anymore and that is forcing oxygen out of the plants? These are bubbles coming out of the plants not the ones that form on everything in the tank.


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post #4 of 12 (permalink) Old 03-29-2010, 11:03 AM
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This is really pseudo pearling. It is just the gases in solution coming out of solution. It is very common after water changes. My tank that does not pearl at all does this after large changes...
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post #5 of 12 (permalink) Old 03-29-2010, 10:33 PM Thread Starter
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Ok, it just appears odd because you can see the bubbles streaming at specific points on the plants-it's not random gases coming out of solution. Maybe when a small amount of O2 is expelled from the plant excess gas in the water gasses out and forms a larger bubble almost like the minute amount from the plant is a seed for gas.


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post #6 of 12 (permalink) Old 03-29-2010, 11:48 PM
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There's so much oxygen that it can't dissolve anymore, so you see it on your plants. Especially from any place the plant was cut. It sure is pretty like that however. The plants are making the same amount of gas, you can just see it now.


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post #7 of 12 (permalink) Old 03-30-2010, 02:21 AM Thread Starter
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Ok, looking for a more scientific explanation. I know that tap water has a higher level of dissolved gas of which O2 is just a component of (nitrogen is a big part of it). Also cold tap water can hold more gas than warmer water so as water temp goes up the saturation point goes down and dissolved gasses come out of solution hence the bubbles on everything (glass, plants ect). Based on the posted explanations when water has reached the saturation point plants pearl but I have plants in my tank that pearl all the time when lights are on. So, is the water saturated with oxygen then? Or are the plants producing O2 at a higher rate than can be dissolved? Any botanists/chemists out there that can explain this in more detail?


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post #8 of 12 (permalink) Old 03-30-2010, 04:41 AM
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Originally Posted by MarkMc View Post
So, is the water saturated with oxygen then? Or are the plants producing O2 at a higher rate than can be dissolved? Any botanists/chemists out there that can explain this in more detail?
When plants pearl, it is not because the water is saturated with oxygen, but because the production of oxygen is faster than the rate at which it can be (passively) diffused into the water column. As a result, you see bubbles.

Don't you notice that after the lights turn off, and the next morning, there are no more bubbles on the plants? This is because the O2 had enough time to diffuse into the water (or perhaps a fish simply brushed past the bubble and caused it to float to the surface, etc).

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post #9 of 12 (permalink) Old 03-30-2010, 04:53 AM
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it's not just O2 that's in new water. There's N, CO2 etc...


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post #10 of 12 (permalink) Old 03-30-2010, 04:58 AM
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The reason for not doing routine big water changes on non-CO2 tanks is that tap water often contains a lot of dissolved CO2. When you do a water change you are adding lots of CO2 to the tank, which soon escapes from the water surface, but it does give the fluctuating CO2 that can trigger algae to start growing.

Compared to oxygen or nitrogen, CO2 dissolves very easily into water in high concentrations, so I would expect typical tap water to have lots of CO2 but not much O2 or N2. That surge in CO2 is likely to be the cause of the pearling after a water change. That also suggests that you don't have enough CO2 in the water before doing the water change, or you would have pearling before the water change.

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post #11 of 12 (permalink) Old 03-30-2010, 10:52 AM Thread Starter
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Quote:
Originally Posted by Hoppy View Post
The reason for not doing routine big water changes on non-CO2 tanks is that tap water often contains a lot of dissolved CO2. When you do a water change you are adding lots of CO2 to the tank, which soon escapes from the water surface, but it does give the fluctuating CO2 that can trigger algae to start growing.

Compared to oxygen or nitrogen, CO2 dissolves very easily into water in high concentrations, so I would expect typical tap water to have lots of CO2 but not much O2 or N2. That surge in CO2 is likely to be the cause of the pearling after a water change. That also suggests that you don't have enough CO2 in the water before doing the water change, or you would have pearling before the water change.
No, I do have pearling before the wc just not the large amount that I witnessed. I have never taken my tap and measured the pH and let it sit for 24 hours and retest. That would give an indication if there is any large amount of CO2 in my tap water. As for CO2 in the tank the 4dKH distilled water DC is green everywhere in the tank I have placed it and I see a .5 to 1.0 pH drop everyday indicated by my controller-2 nano & 1 conventional power head for circulation in a 55g. However, your explanation seems the most plausible to me-CO2 in the tap water.


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post #12 of 12 (permalink) Old 03-30-2010, 11:01 AM Thread Starter
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Originally Posted by Darkblade48 View Post
When plants pearl, it is not because the water is saturated with oxygen, but because the production of oxygen is faster than the rate at which it can be (passively) diffused into the water column. As a result, you see bubbles.

Don't you notice that after the lights turn off, and the next morning, there are no more bubbles on the plants? This is because the O2 had enough time to diffuse into the water (or perhaps a fish simply brushed past the bubble and caused it to float to the surface, etc).
I understand what is behind the mechanism of pearling. My question was to posters that suggest that the excessive pearling is because the water has reached the saturation point and can't dissolve any more O2 causing pearling on the plants.


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