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Pearling after a water change? Why?

Just as an extra, I've just checked again at what is almost 90 mins after the removal of the jug and this is what it is like now. The patch to the right that wasn't exposed is just starting to pearl now although you can't see it here.

aaronnorth said:
That is very interesting atlaafe.

Matt, i am not sure by the pressure in the pipes etc. But what i believe is that the water is O2 saturated, then this comes out of aqueous solution, and into gaseous solution (this then appears as pearling). I sometimes get bubbles on my glass after a water change, so this could still be in the question.

But the exposed to air method introduces 'real' pearling, whereas the O2 saturation is merely O2 from the water.

yep, exactly.. this is what I mean.
Nice one altaaffe. That was some good thinking.

Very nice experiment - good thinking.

When I use colder water for the w/c than I have in the tank I get pearling everywhere, on hardscape and hardware also. I understood this is because the cold water heats up and can carry less dissolved gas, so it comes out of solution as micro bubbles?

If I match the temperatures I only get a little bubbling on leaves - could this be due to increased CO2 in the w/c water? I'd have to leave the water to stand overnight to test this for sure but don't have a big enough container.
Very good experiment. I'm thinking the same as Matt though.

I don't question Tom's theory in that yes it is obvious that the plant is pearling from exposure to the air. I'm not so sure it has a 'growth spurt' like he says in the thread though.

The under the waterline is the thing to find an answer for though. The question was about pearling after a water change. We have an answer for the plants above the water change level but none for the glass or under the waterline yet.

I'll be doing my 20% change just before 3 today and that will expose only the tips of some of the ferns so if there are loads bubbles lower then we still have a question to answer. I'll do the same observations with 50% change tomorrow.

This theory of Tom's also ties in with the emersed growth startup that people have recently been using. The plants in theory would grow nice and fast at the beginning. Faster than starting the tank filled!!!

Could you try filling the jug with tank water,doing a water change,letting the water settle for a few minutes then removing the jug.I'm fairly convinced it's air in the water being replaced as my plants are covered in bubbles after a water change.
But then was it not also suggested that because those plants have had a big gulp of CO2, that they don't take as much out of the water stream leaving a higher concentration for the other plants?

The HC to either side of the affected area started pearling more and sooner than areas a little further away - just a theory as I don't have enough drop checkers (or the accuracy) to see what the exact CO2 level is all the way across.
Could well be. Tom has tested his tanks with his gas thingywhatsit and says the ppm of CO2 changes significantly away from the diffusion area. Can't remember the figures but the differences were quite surprising.

Wouldn't explain instant bubbles after the water change on crypts and ferns that I've just got though!!! Will take some pics for the first few hours before posting the lot. lol

SuperColey1 said:
Wouldn't explain instant bubbles after the water change on crypts and ferns that I've just got though!!! Will take some pics for the first few hours before posting the lot. lol



but if we knew it all straight away, there'd be no discussions on the forum :lol:
This is 2 hours after my water change, as you can see there are bubbles on my equipmment. So this could prove the theory of O2 saturation in the water, (where it forms on the plants after coming out of aqueous solution and appearing as pearling)




So perhaps it is a miture of the two? The taller plants that have access to CO2 in the air is 'real pearling' but lower plants like HC is 'fake' pearling from the oxygen in the water.
So another non scientific test that proves nothing but a 'few' pics to show what little happened ;) Water change was immediately when the lights came on.

This shows the tank level pre water change:

This is the level after 20% removed:

And here you can see that hardly any plantmass is above the water level. Just a few fern tips and a bit of Koralia:

These pictures are all from an area of fern that even with the lower water level was at least 4 inches below the water level. With the tank full this about 6 inches from the surface.

This is showing there are already bubbles immediately after the water change. No time here for real pearling:

This is a similar area 1 hour after w/c:

This is a similar area 2 hours after w/c:


To compare this is a similar area on non water change day after 5 hours of the photoperiod to gauge the amount of 'real' pearling without any 'fresh' water to enhance the bubbles:

What does it prove? No idea. lol. I think we can see that indeed after a water change that the bubbles on the leaves are there and some appear immediately. They accumulate as time goes on just as pearling does. However my tank normally starts to pearl 4 or so hours into the photoperiod and the water change was done at the start of the photoperiod. Virtually all the plants weren't exposed during the water change. In fact the crypt Parva and Wendti on the substrate have bubbles under their leaves but my camera/photo skills aren't good enough to capture these ;)

I am assuming that over the 2 hours the gas in the water has gradually collected under the leaves when coming out of solution?? No idea. That is for the scientists to discuss.

I didn't get round to doing a 50% water change today (cleaning the oven took over. lol) and don't think that I will need to r.e. this subject. lol I think doing a 20% change yesterday showed that 'pearling' started earlier on plants below the water level at all times so it just needs clarification on wether it was pearling or just O in the water.

However whilst I was at the sink and oven for 2 hours I was thinking boring thoughts. lol

From my understanding of the 'scientist' type threads that I don't understand (if you get my meaning) we have it drilled into our regime the need for stable CO2. My understanding is that the plants adapt to the CO2 level (rubisco) and aren't growing whilst adapting. Therefore if we are saying that the exposure to a much higher level of CO2 is what is causing the pearling would this not contradict the rubisco/adapting theory?

Surely if going on this adaptation stops growth theory the exposure to higher CO2 would mean that indeed the plants would have to readapt to the new levels meaning they wouldn't grow and therefore wouldn't pearl either?

Have I got this completely wrong?

I was under the impression it was adapting to low levels of CO2 that caused a problem. High levels (i.e. 30ppm upwards) will allows the plant to gather more CO2 and grow more effectively whereas lower levels mean the plants have to adapt and put more effort and energy into acquiring enough carbon for growth.
So is there not max level of growth then?

By this I mean that if I have 30ppm and dose EI under low light then would my plants not already have all the CO2 and nutrient they could possibly need for the light provided?

Would they not already be growing at the maximum they could with the low light they are getting and therefore couldn't grow any faster wether more CO2 is available or not?

I am thinking that the 'early' pearling is assuming that they get extra CO2 and therefore have a growth spurt but surely the light level would determine the speed they could grow and if the light level is low.

Coming from the point of view of my tank, I dose and inject at the same levels as a highlight tank and therefore there 'should' always be enough in there of both C and nutrient to be at full speed growth already.

All plants are CO2 limited, even terrestrial ones, partly as the enzymes they use all evolved during a time when the CO2 concentration was much higher and they evolved to utilise that. I think plants could use more than 30ppm if the light allowed, but the fish would die! I don't think we ever actually 'max-out' growth, just provide enough CO2 and nutrients using EI to mean that the light levels now limit plant and algae growth and the plants are better at using the light.

What I understood was that as plants have evolved to deal with lower and lower CO2 levels mutations have been selected that code for new enzymes or more efficient structures to increase the efficiency of the Calvin Cycle. In higher CO2 levels this process becomes less costly, therefore the plants are more efficient at capturing carbon and have to use less energy to do it. Other things may then limit growth such as nutrients or light. I think that low or fluctuating levels of CO2 mean that the plants have to commit a lot more energy to capturing enough carbon, slowing growth and allowing algae to gain a foothold. At higher CO2 concentrations these problems are less likely to happen.

Going back to pearling I don't think that actually has much to do directly with CO2 levels at all. I think the thing that governs whether you get pearling or not is purely the O2 concentration in the boundary layer around the plant. Up the O2 levels in the water, either by adding O2 rich water or the plants producing more O2 from good CO2, light and nutrient levels, and the plants are trying to get O2 to dissolve into already saturated water which can't happen so O2 bubbles form. So according to that exposing the plants will up the O2 the plants produce and adding new O2 rich water will increase the amount of O2 already in the water hence a 'double-whammy' of why you get pearling after a water change. Also the bubbles on the hardscape are because as the cold, O2 rich water warms the O2 becomes less soluble meaning the water is now saturated and some O2 comes out of solution onto the non-living things in the tank.
Sounds like a good sound case to me Ed.

I've posted in Aarons post about HC emersed but when I introduced a tiny lump to my nursery above the O tank I couldn't believe the growth rate. I've got plantlets from planlets of cuttings of staurogyne taken from the tank that are bigger than the original plants. These have no extra ferts only what comes from the Oscar & friends but an abundance of CO2 with being grown emersed.
So what we are in fact saying is a mixture of the following:

That if plants are above the water level they can take in 'surplus' CO2 and when they are submerged again this means that they don't necessarily grow faster but because the fresh water has more O in it than normal that the plants excess O 'pearls' earlier as the water already has too much O within it?

That low light or highlight doesn't really count for anything at apart from speed of growth and that CO2 is the key factor?

Under this theory of more O etc producing pearling this would explain that with me always having high surfact turbulence that this is why I get pearling under low light when even some highlight people don't? Assuming here of course that my turbulence having the lily pipe slightly above the surface is pulling more O in than the standard 'old way' of zero surface turbulence?

Either way I'm not overly concerned. I just remember when 'pearling' was the holy grail for many believeing thta pearling meant a really healthy tank whereas over time I think we've all had Riccia, we've all seen pearling and aren't as fascinated by it anymore. What we are now saying is pearling or not doesn't mean a healthy tank because dependent on your setup and routine pearling may not necessarily be possible (thinking a healthy growing tank with low % or zero water changes and zero surface turbulence.)

I don't think you relate this to growth Andy. Growth is dependant on a whole range of factors. We are talking about the rate of photosynthesis (and the related production of O2 from that) and the amount of O2 in the water creating locally saturated boundary layer around the leaves.

Plants may take in slightly more CO2 from the atmosphere as the atmospheric CO2 is about 385ppm whereas we only have at most 30ppm in our tanks. This then allows those plants to photosynthesise more effectively after being exposed.

Light will be a factor as light also governs the rate of photosynthesis. But good light can't do it without sufficient CO2.

Even the turnover will play a role as very rapid turnover will reduce any boundary layer around a leaf so reducing the chance of it being saturated with O2. Also the shape of the leaf will. Maybe this is part of the reason why liverworts and mosses always seem to pearl so well - their leaf structure leads to locally saturated pockets of water.
Hmmmm. I think the science is getting a little beyond me here. lol But I do understand basically what you are saying.

Different plant shapes etc I see in my tank that anubias may have 1 single large bubble under them whereas the ferns are covered in bubbles. similar with crypts they seem to take longer than the ferns.

I think I shall leave the conclusions to those in the know on this one as it will get over my head soon :lol:

Will continue to read with interest though ;)

Oh no you all say. Yes I have another query on this subject!!!! :lol:

Maybe this one does dimiss the theory of 'real' due to exposure to the air :wideyed:

I have just done my 50% water change that I didn't get round to yesterday. As I usually do I did it well before the photoperiod. So the previous photoperiod had ended 11 hours previously and the water change done 4 hours prior to the next photoperiod.

Upon looking into my tank the leaves are covered in bubbles??? :?

Can this be pearling as per the exposure theory? My guess is that it can't be. Would this also dispell the theory totally or just add another thing to consider into the question?