Plant damage(?) at base

[Delapool]

If it is a question of CO2 levels throughout the tank, then placing drop checkers on either side (and maybe one in the middle) should help prove/disprove this. With proper circulation this should not be the case.
Are you actually seeing different growth rates with identical plants in different parts of the tank (assuming left side/right side)? I am late to the party and have not scrolled through the entire thread.
I have seen the above occur but it was due to shading from other plants primarily and, to a lesser degree, distance from the light fixture. Meaning, those directly under the light fixture did better than those further away from center. The plants I am referring to are low growing foreground plants.
I believe swords can tolerate low light but do better in low medium+. Bacopa caroliniana (and possible other Bacopa species) have grown well in low to medium high in my tanks.


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I do have spare drop checkers so could try this.

It's hard to say on plant growth as generally I've tried different plants on either side. Previously the right side had val and ambulia growing ok.

The central back of the tank under the glass cross-piece grows well.

The left side does get some pearling whereas on the right side I've never seen this.

The plants are breaking off at the base on both sides though. I've got no snails in the tank now (that I know of). The only fish (assuming they are contributing) I can think of would be the bn catfish.

 

[Delapool]

I would try not to focus on lack of co2 in the tank as a whole but rather availability/competition of co2 in certain areas of the tank.

Different plant species have different carbon affinities which means their uptake and requirement vary. Other things that change co2 uptake as you know is light.

As fresh has mentioned and Tom Barr reiterates quite frequently is try not to focus on PAR but uniformity of PAR at substrate level. You can only measure this with a certain degree of accuracy with a PAR meter. If light is uniform co2 needs to be uniform too as in circulation and transportation of the injected co2 needs to be distributed evenly which becomes more problematic as the size of tank increases.

Thinking about what we have mentioned so far. The plants on the left are in direct contact with co2. How much co2 is off-gassed by the time it reaches the other side?

Plant mass as a result is much greater on the right which means more uptake/diffusion of co2.

How much co2 is dispersed by obstructions in the tank (wood) before it reaches the far end. How many dead spots are there in the tank? Think about the hydrodynamics (fluid flow), is the motion of flow going in the right direction etc?

Many enthusiasts with such large tanks take hydrodynamics very seriously and a problem would probably only rear its head in such cases.

Can you switch the co2 system to the right side of the tank?


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I do have a backup co2 bottle and tunz co2 reactor so could see about sourcing a solenoid for this. And run co2 either side.

Or get a line splitter - actually that would be fairly cheap.

Thanks I'll have to have a look at flow.

I've got the PAR meter working. Just need to borrow a laptop from somewhere so I can get test readings quickly and start going through ideas.