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Algae invasion pet shop plant tank

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Hi guys,

I could really use your expertise now. I have a pet shop in Sweden together with my wife - cat/dog is her part and mine are fish and plants. Our aquarium plants never did any good in the fish tanks, naturally, so about a year ago we started up a dedicated 720 liters tank just for the plants (potted plants). We went all in and installed a co2 tank, good lightning and PMDD fertz. At the beginning all was good as the plants no longer died; on the contrary they started growing, A LOT. But growth is not always good in a pet shop, at least not too much growth, because the plants look nice at the top and less so at the bottom. Hard to sell to a customer in other words, even though they are healthy. So you want moderate growth, but above all, you want algae free growth! And that's where the real problems come in. The leaves of almost all plants get a dark green/brown color, not lush light green, and also gets black/dark grean algae spots. From a distance, the whole tank looks murky. Only the new arrivals look fresh. Give it a couple of weeks and they start to look bad too. In the link below you can see some pictures of how it looks:

https://www.dropbox.com/sh/j5b8ukgeu7n9bgg/AAC2BoH5GVLuoK5d-rv2CQzAa?dl=0

Some details of the tank:

Size: 720L

Lightning: 4 fixtures, each 2x39W T5 with reflectors (hagen glo), life-glo T5 tubes.

CO2: approx 30ppm

Other fertz: PMDD. I add KNO3, KH2PO4, K2SO4, Mi+. Here I don't really know the levels, I googled the following recipie (for 500ml bottle):
KNO3 25ml
KH2PO4 5ml
K2SO4 5ml
Mi+ 25ml
From these bottles I dose 150ml KNO3, 150ml Mi+, 90ml K2SO4, 60ml KH2PO4 once a week after a 50% water change. One might ask why the different levels for differnt fertz, that's because I have had trouble before with too much P in the tank, but that might be a mistake, I don't know.

Other: to keep the pots nicely lined up, I use a garden fence with square holes in which the pots fit perfectly. I think it's made of iron with some kind of plastic coating to avoid rust. Could this cause any harm?

Please help me out here. Is there an obvious mistake? Any pointers? Suggestions? I can't keep loosing plants like this, I'm going mad!

Best Regards,
Mac
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In a store I am sure the tank gets a long photoperiod.
Dim lights and cut back on ferts until a compromise is found.

My wife has a low tech 20G tank, 9-1watt 7300K LED's.
All plants grow but much slower and without ferts.
No plant algae, and moderate glass cleaning.

How deep is 720L tank?
Our LFS has shallow tanks for their plants and not to good lighting.
 

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Like others have said I would cut back the photo period. Run an 8 hour grow cycle with full lighting and the rest of the day run minimal lighting to display the tank. If your tank is without fish you can increase the CO2 beyond 30ppm and that should help also.

What type of filtration or circulation do you have in the tank? I would try and run a few circulation pumps if you don't already have them. Something like the hydor korilina nano. You can put a filter sock over the hydor to help catch detritus.
 

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Stainless steel seems to be OK but other metal exposure is not good.
But I'm fairly sure this would effect fish more than plants.
That tank is shallow for that much light. Is that all end to end or two rows ?
Sounds like two rows of 36" bulbs.
Because of the long shop hrs, get some fiberglass window screen and put it over the top but under the lights. One piece cuts the light by aprx 30%.
 

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My first though was a deficiency. Can you remove the 'algae spots', or would you say the darkness is inside the leaves?

Here are the weekly dosing numbers:
Nutrient - ppm/week
NO3 - 6.64
PO4 - 0.65
K - 5.18
FE - 0.2

You have quad T5 and lots of CO2 - could you be nutrient limited given the high amount of light you have (and how long is your photo-period)? The dosage above is very lean.

Maybe a better way to limit growth is to take away 1 or 2 T5 fixtures (run on only 2 or 3 fixtures).

Do you have a test kit which can measure nitrates and/or phosphates? If so, it would be interesting to see if these are reaching zero as you approach your next water change / dosing day.
 

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Discussion Starter · #7 ·
Hi all,

The measurements of the tank is 200x60x60, and the lightning is arranged in two rows, like this [==]. As of last week, I removed two of the tubes so now I have 6x39W of T5 lightning. Maybe that's overkill too, even though the tank is quite deep. As I said, the goal here is a slow but healthy lush green growth with a minimum of algae.

A Fluval FX-6 is used for filtration and a Tunze nanostream helps with the circulation.

I was out of phosphate measurement kits in the shop today, but I measured Fe and NO3 and got ~0.1mg/l and ~25mg/l respectively. A bit short on iron I would suspect, but could that really be the root cause of all my misery? I dosed fertz yesterday so we'll see how these levels change until the water change next week.

imcmaster: You say the dosage is pretty lean. What would you recommend? Do you know a good source of information regarding how to dose PMDD? And I know I dose phosphate with causion, maybe that is a mistake. Could that cause these kind of algae? The dark spots I would say is on top of the leaves, not inside, but still they are hard to get rid of, not like brown algae.

Regarding the photoperiod, our opening hours are only 10-18 so that should not be a problem. There is no outside lightning getting in.

:help:
 

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I'll look up the PMDD, but in the meantime lets focus on PO4.
I think your algae is GSA (Green spot algae). One cause is very low PO4.
Once you measure the PO4 you can confirm. All this might be solved by bumping up PO4 a little bit. Cheers.

PMDD link:
http://www.theplantedtank.co.uk/PMDD.htm

Here is how your dosing compares to his PMDD formula (extracted to weekly dosing):
NO3 - 10.5 ppm (your dosing is 63% of that)
PO4 - 2.8 ppm (your dosing is 23% of that)
K - 11.2 ppm (your dosing is 46% of that)

If you assume your tank is not 100% fully plant, then your NO3 and K are probably in line, but your PO4 is very low relative to his dosing.

The link discusses GSA as a typical symptom of dosing PMDD, and the need to adjust PO4.

What problem did you have when PO4 was dosed higher?
 

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Discussion Starter · #10 · (Edited)
Hi, today I made som measurements and here are the results:

PO4: 0.25-0.5mg/L (really difficult to distinguish between these two colors)
NO3: 10-25mg/L
Fe: 0.1mg/L

So nothing was bottomed out completely. It did also look a little bit better this week as I didn't notice any new algae on the new plants I got last week. Maybe to early to say. Could it be that I was low on dosage before, and with the reduced lightning the dosing was ok? Anyhow, it seems that you think it is better to have a little to much than to little so I increased the Mi+ dosage by ~20% and the KH2PO4 by ~50%.

Any thoughts?
 

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There are two factors at play: Lighting and fertilization. When you reduce lighting, the fertilization demand will go down accordingly. Perhaps just reducing the lighting would have been enough.
However, it is known that when you have a lean dosing strategy, and the ratio of Nitrates to Phosphates is high (like your tank was), then GSA is likely to appear. The fix is to increase PO4 until the GSA disappears.
I think you are on the right track back: You have reduced the lights, and you know that if GSA appears again, to keep on track of the PO4 measurements and increase it slightly until GSA is gone.

It will be good to hear others opinions as well. Good luck with your plants!
 

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Just a thought, depending on the tanks general perimeters, but the other thing would be to add an amano shrimp clean up crew. They are fairly big (in comparison to cherries) so should be easy to avoid when taking out plants to sell but may help keeps things smarter looking.
 

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I've read it somewhere in this forum before but when selling aquarium plants in pet shops, the idea is not really to make them grow but to keep the plants alive and in the same condition as when they came in - green, algae free, and somewhat "fresh" until they're bought by customers. so decrease the lights, the amount of fertz and also the temperature a bit to slow down their growth.
 

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Discussion Starter · #14 ·
There are two factors at play: Lighting and fertilization. When you reduce lighting, the fertilization demand will go down accordingly. Perhaps just reducing the lighting would have been enough.
However, it is known that when you have a lean dosing strategy, and the ratio of Nitrates to Phosphates is high (like your tank was), then GSA is likely to appear. The fix is to increase PO4 until the GSA disappears.
I think you are on the right track back: You have reduced the lights, and you know that if GSA appears again, to keep on track of the PO4 measurements and increase it slightly until GSA is gone.

It will be good to hear others opinions as well. Good luck with your plants!
Thanks, let's hope the problems are solved now =)

Just a thought, depending on the tanks general perimeters, but the other thing would be to add an amano shrimp clean up crew. They are fairly big (in comparison to cherries) so should be easy to avoid when taking out plants to sell but may help keeps things smarter looking.
I've already got that =)

I've read it somewhere in this forum before but when selling aquarium plants in pet shops, the idea is not really to make them grow but to keep the plants alive and in the same condition as when they came in - green, algae free, and somewhat "fresh" until they're bought by customers. so decrease the lights, the amount of fertz and also the temperature a bit to slow down their growth.
Yep, that is the plan. But still I don't want to have so little light that I can't have the more demanding plants without them dying.
 
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