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[APD] Re: Acidity in a Discus tank

>The  55 gal tank I'm inquiring about has been set up as a rather prolific
>planted Discus tank, both plants and fish, for a very long time.  There is a
>pair in there now spawning.  It has about 10% of it's water changed daily
>with RO water.  I occasionally add RO right to the tank, something I seemed
>to have overlooked for a while now.  

Well, this goes back to the basic simple concept: plant health. There's no reason to spawn Dicus at 4.5-5.5. They spawn well at 6-6.5. I've done it without even trying............at 6.7ph/GH 9 /KH 5.5 and dramatic plant growth.

I think many discus folks place barriers up where there are not any. They come from a moderately variable environment, not ultimate stability, they are flexiable, they are big old cichlids, not wimpy touch fish that die if you look at them wrong. 

I would suggest adding CaCl2/MgSO4 or SeaCem Equilibrium to raise the GH to 5.
I would add at least a KH of 2. Baking soda or simply blend your tap water with RO to get the serised GH/KH combo. 

 I noticed that the tank seems to be
>experiencing an undue spurt of algae growth lately and after measuring a few
>parameters this morning it occurred to me that perhaps the unusually low Ph
>and KH might have something to do with it, all other things being the same.

I would say the cause is poor plant growth, that's where I would look.
Adding lots of organic waste at high temps will cause issues with reduction which seems to be your case.

Like adding more light, adding too much waste makes things more difficult as you increase the loading on the tank.
Your saving grace is daily water changes, but if you did larger water changes, this would mitagate this waste issue further and would stabilize.

So that would be one option.

Like adding more light, adding higher temps also increases the rate of plant growth and the demands associated with that.

82-84 F would be another option, Discus bred fine at this temp for myself and others.
If breeding is all this is about, go barebottom tanks, otherwise provide some flexibilty to a fish that is quite able to tolerate a wide range of conditions but in the aquarium and in the native ranges.
If you use plants to provide a good habitat for your fish, they should be the focus.
Healthy plants= healthy fish.
Algae are excellent signs of sluggish or otherwise poor plant conditions.

>Interestingly enough I have another tank on the same water changing schedule
>with mostly South American tetras and angels, and similar water parameters
>with very manageable algae.  The only difference I can ascertain is the
>water temperature, 76 instead of the 86 in the discus tank.

See above. Higher temps= high nutrient and metabolic demands on fish and plants.
Having a high temp also means less O2 and CO2 (any gas) at equilibrium, so gas is harder to keep in solution.
Both CO2(plants) and O2(fish) polay important roles.
There are limits to this, fish will not do as well at 76-78, but meeting in between will help.

>After rereading your email it occurred to me that there is one other
>difference between the two tanks that I failed to mentioned.  The one
>experiencing the problem has a flourite substrate and has been the less
>stable of the two tanks on the automatic RO water changing system since
>switching it over from gravel several years ago.

Doubtful this has much significance......

>According to the graph at:
> phosphorus availability is at one of it's lowest points at precisely the ph

Well do add PO4?
Or rely of fish waste alone?
You do daily water changes and unless you add the PO4/NO3 back in some form in a relatively decent ratio so they do not become limiting, you are lowering PO4 availablity that way much more so.

And another thing..........we are discussing aquatic plants and water column uptake, not terrestrial agricultural food crops.

Apples and oranges.

>You intimated that the rate of aluminum phosphate fixation was dependent
>upon having a clay or fine mineral substrate.  Why is that?

Al reduces(provided you have it available to reduce) and can bind the PO4. If you don't have it, it will not bind. You need an acceptor and donor. There are other things such as FePO4 that can form.
Do you have clay?

The thing is that the plants will have first access to any water column source of PO4, the flux in/out to the clay is slower than in the water column. So this should not limit the plants through PO4.

If anything..........Al3+ toxicity plays a much more dominant role at low pH's than PO4 binding issues in wetland soils.......regarding plant health and growth.
You can dose KH2PO4 to the water column and test this easily for your self and see.

Steve still believes plants prefer PO4 in those clay balls. I would challenge that and that plant growth is better(faster relative growth growth). You can also mmaintain a more stable level of PO4 through the water column and you can also test it's levels there easily. Reducing compounds such as organic waste also do not build up in the water column to the same degree as the substrate. So PO4 will be more available if you take that logic to it's final conclusion............ 

>I'm sure that the topic of phosphate availability and it's effects on plant
>and algae growth have been addressed here before, and if so I apologies for
>posing the question to the list again:  If the problem turns out to be
>phosphate fixation due to low ph with a clay substrate; does a high
>temperature, phosphate deprived environment, favor the growth of algae over

Anything that reduces plant growth, favors algae growth except light...........
This includes people moving their plants around a lot and disturbing the tank a lot.
As well as not enough PO4 for the plants, you will not limit the algae through PO4 limitation, you can try, better get some top research grade lab equipment, I mean the best research stuff out there. 
Plants need more PO4 based on dry weight ratios, based on their niches, based on lake studies(several hundred at least) and based of enzymatic uptake kinetics.

Give the plants what they need to grow.

>If not, then the problem might simply be the lack of minerals such as mg,
>ca, k, etc. from the failure to replenish them at more regular intervals.

Also likely part of the problem.

>But then the question of why the instability in the clay substrate tank and
>not the gravel tank, with the only difference being temperature, would still

Vacuum the gravel in small 1/4 tank sections each week.

There is not set and forget substrate, they need some mainteance to run well.
Removing excess mulm/detritus once every year or two helps substrates from souring. This allows more flow in/out as well.

>However, if algae can thrive in a phosphorus depleted environment, the lack
>of which a result of being fixed in the form of aluminum phosphate due to
>those occasional (rather long) periods of low ph coupled with a clay
>substrate, it certainly would explain a lot!

Well it would be easy to see if your plants are PO4 limited, but you do not know if that is the case due to clay binding with the PO4 from fish waste or KH2PO4 dosing.

Plants respond to dosing of KH2PO4 in 30-40 minutes, I highly doubt the clay in the substrate in a high bioload tank is going to have a chance to bind the PO4, and after doing this for so long, the clay will be all filled up with the PO4...........

Clean the tank well, Vac the 1/4 sections, lower the temp down a tad, add some KH2PO4/SeaChem EQ, do a few larger water changes, blend with tap to get decent GH/KH(why remove something then add it back?).

Happy plants= happy fish. I have not lost fish nor had a disease for over 15 years doing this.........
Altums, Discus, most SA fishes......

Tom Barr




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