Difference in drop checker readings in different positions

Aeropars

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Hi Guys,

I've got an observation which has me curious.

I moved my drop checker to the other side of the tank the other day as its easier to read.

I have 2 filters. 1 eheim internal and the built in juwel filter running. The internal is fitted to the right side of the tank blowing directly out the hole to the left side. The eheim spraybar is on the left of the tank blowing from left to diagonally down/right. I thought my flow was pretty good as you can see plants on the bottom of the tank moving.

I originally had the drop checker on the right of the tank which showed a pretty bright green. I then moved it to the left under the spraybar and have a pretty dark green now.

So how come, even though my flow appears to be pretty good, is this small area of the tank not having as much co2 in it?. Could it be that small co2 bubbles which come out my filter outlet (using an aquamas inline reactor) are going into the drop checker thus increasing the concentration of co2 in the drop checker (based on the fact that a pure co2 bubble will be more gas than whats dispersed out the water) or do i really have bad flow?

Lee
 

GreenNeedle

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Is the lighting exactly the same in the 2 positions? Is there a plant reflection anywhere near one of the positions?

If I put the DC on the open right of my tank it can read blue which is the true reading. If I then transfer it to the left it looks green even though the nearest leaf is approx 6 inches away!!!

Either way the best position for permanence would be the furthest away from where the bubbles start so watch the bubbles in the flow and put it where it ends. I would suggest not to put it exactly opposite where the bubbles are dispersed because then they will be pointed directly at the DC.

AC



Doesn't hurt to move the DC around though and then go by the lowest reading.
 

Aeropars

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HI,

Yes the lighting is the same across the entire tank and i can confirm its not distored by coloured backgrounds as before it was in front of the black internal juwel filter so i this was the case it woudl be lighter now, if anything.

When I say the bubbles, this are intermittent bubbles spurted out the filter outlet, not a constant stream. I dont use an external diffuser, only the inline aquamas one.

Here's a graphical view of how its set up:

untitled.jpg
 

ceg4048

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Lee, it looks to me like the the two flows have some cancellation effect because they are opposing. This doesn't appear to be the most efficient use of the filter effluent. Both filters should point in the same direction so that their flows are additive, not subtractive as presently configured. Also, flow along the long axis of the tank isn't the best use of the energy as there is loss of momentum along this axis due to distance and friction. I suppose aesthetics come into play here, so you may prefer this configuration visually, but from an energy standpoint it would be better in general to send flow across the short axis. The problem with that is that you'd need a second bar to cover the length.

In any case it's not surprising at all that the dropchecker mounted against the far wall registers higher concentrations. It is very difficult for CO2 laden water to rebound from the far wall and return to the near wall at the same concentration because of this distance. In any case the distribution of CO2 in a tank is never homogeneous. Barr's measurements reveal that the concentration leaving the spraybar exit is typically about 10X higher than what can be found in some of the plant beds.

Cheers,
 

Aeropars

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Hi clive,

Thanks for your input.

I could have really done wihout the internal being in there but as the tank evolved into a planted tank I never really thought about getting rid of it. I guess if I can get it right then it will help the flow.

I'm not quite sure what you mean about the axis of the tank. Am i right in thinking you mean it not being efficient when the filter output aims at the widest length of the tank rather than the shortest? If so I'm not sure how I could acheive it.

I was thinking about maybe going down the lily pipe route but thats an additional cost.

Can anyone suggest a better way of setting up the flow using the existing equipment?
 

ceg4048

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Yep, 3D space is defined along 3 axes. Length is the X axis, width is the Y axis and height is the Z axis. You can define flow to the right as being positive flow and flow to the left as being negative flow. Your setup has the internal filter's negative flow subtracting from, or interrupting the positive flow of the spraybar along the X axis. Have you ever tried spitting into the wind? How far does the spit go? The energy of the wind is against the energy of your spit. Now turn around and spit in the same direction as the wind. You spit carries a lot further then, doesn't it? If you're spitting at a wall wouldn't it be easier if the wall was closer?

So you have two things working against you in this setup: 1. Opposing flow each weakening the other, and 2. Long distances which dissipates the energy. These aren't the only factors and they may not even be significant if other factors like pumping capacity aren't addressed.

It's easy to solve item 1. - just move the spraybar on the same side as the internal filter. so that they both work in unison instead of interfering with each other.

Solving item 2 is less obvious, but think about drawing a circle with the flow. Since this is a confined space we want to create a smooth repeatable pattern of flow. Instead of a violent collision meeting in the middle of the tank it would be better for the water to move in a circle. If your pattern is on the long axis this would have to be an oblong circle so the flow would carry from left to right, then travel down along the right wall and then travel along the substrate from right to left and then up to the surface on the left wall. That's a long way to travel and demands a much higher energy level to complete that path. In a small tank that's easy because the distance is short and filter forces relatively high. As the tanks get bigger though this becomes more difficult to accomplish, so you need much higher pumping capacity.

If you have flow along the shorter axis then the energy doesn't stall. The energy of the flow can make it more easily to the front glass. Looking from the left side glass, you can achieve a clockwise loop, so flow impinges on the front glass still with plenty of energy, is deflected downwards, reaches the substrate where some is deflected towards the back glass and then upwards along the back glass.

You can see here that the spray pattern is over these plants and doesn't need to be directed at them.


But this short axis loop pattern has to extend along the length of the tank to be really effective.


A wider view. This is 6 feet worth of tank and 5 feet worth of spraybars.


Put your sunglasses on! This shows the impingement energy against the front glass which is deflected downwards.


As you can see, the orientation of the spraybars is that they point horizontal. There is no need whatsoever to aim the flow downwards because the impingement against the glass does the work for you. Because the flow is horizontal you can achieve maximum surface distortion to break up surface film. No lily pipe can do this. I don't care what the marketing department says.


You still do need to come close to the 10X rule, and your CO2 injection techniques must be adequate (in this case I have external reactors) but this configuration can work quite well. It will produce even and consistent flow and deliver nutrients effectively to the plants so you don't need to buy contraptions like skimmers or fancy overpriced glass lily pipes - just a couple of plastic tubes with holes drilled through. I would definitely encourage you to ditch the internal and get a second external (or ditch both and get a larger capacity external).


Cheers,
 

Aeropars

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Thanks for that clive. I thought thats what you meant but dont want to get it wrong yet again.

I think i'm well off the 10x capacity. I use an eheim pro 2 which is rated at 950 lph and the tank is 180 so i'm at around 5 x flow. I'm not sure what the powerhead in the internal is rated at off the top of my head. What i can do is direct the output of the internal at the front glass and then work on getting the spraybar to do the same.

How did you extend the spraybar? Can you get extension kits or something? I'm so short on cash at the moment i cant see that i'd be able to get a new filter anytime soon unless its pretty good value. Any suggestions?
 

GreenNeedle

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get 2 spray bars. fit one to the eheim and the other to the internals outlets and then fix them side by side at the back (or join them even)

AC
 

Ed Seeley

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Aeropars said:
I think i'm well off the 10x capacity. I use an eheim pro 2 which is rated at 950 lph and the tank is 180 so i'm at around 5 x flow. I'm not sure what the powerhead in the internal is rated at off the top of my head. What i can do is direct the output of the internal at the front glass and then work on getting the spraybar to do the same.

The internal on the Rio 180 is a 600lph pump so you're at about 1,550lph.

Personally the cheapest way to solve all your flow problems would be to fit a hydor koralia, but it means more stuff in the tank! I have just a Koralia 1 and the internal filter in my 180 and it does a great job. The flow from the koralias is a broad steady stream and really mixes the water up well. You don't need extra filtration, just to sort the flow out.

I'm probably going to get another koralia for my other 180l tank (which has a 2128 on it at the moment) and it needs extra flow to sort out a few algae problems - no need for any extra filtration.
 

Aeropars

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Thanks guys.

The hydor thing looks like it could be the short term answer but i guess I'm in the position of a lot of people who migrate from tropical tanks into the planted hobby in that you tend to get inferiour equipment.

Tanking into account the current equipment and configuration, how would you recommend i set it up with the addition of the pump?
 

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