Help! Stunted growth / old growth browning - Low Tech

CARLOSII22

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15 Jul 2020
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I hope everyone is doing well. I have done a lot of reading across the forum to try and troubleshoot the issues I am having, but I am currently struggling with stunted plants and old growth dying off in my low tech tank (no pressurised CO2, no liquid carbon). It has an inert gravel substrate, so I think I may need to water column dose even more than I have been. I understand from reading various posts that nutrient rich substrates aren't necessary if the water column is sufficiently dosed.

I suffered for a long time with no growth at all on all of my plants. Since I upped the magnesium and potassium dosing I have definitely seen a lot of improvement with new growth, especially on my Java ferns and Dwarf sag. I am however still noticing that old growth is turning yellow/brown and dying off on my L. Sessiflora. The new leaves on the majority of my rotala stems are also very small, what is strange is that a select few stems are growing nicely. Likewise with the L. Sessiflora, one or two stems remain a lush green but the remainder only have lush green new growth. I had a decent carpet of S. Repens growing, but the old leaves were dying off and then being attacked by BBA so I cut it all back and replanted, but have yet to see it come back to life.

Please see my tank / water parameters below. I have added some Salvinia to a breeder box to do a duckweed index check and I am seeing the same thing, there is new growth, but old growth looks to be dying off/melting. I think this is a potassium deficiency, but I am keen to hear everyone's thoughts. As it is old growth that is affected, I think it is a mobile nutrient issue. I have ruled out N and P based on testing and the fact that I have high fish stocking and only a moderately planted tank. K and Mg were the other two possible reasons, and I am dosing these now at 10.5ppm and 5.6ppm respectively per week which did help, but I am wondering if I need to dose even more K. With spray bars across with the length of the tank I have good flow around the tank with plants at the substrate level swaying in the flow and a light ripple at the surface for gas exchange.

[Edit]: Changed the format of the information below to fit with the forum guidelines:

1. Size of tank: 275L, the tank has been running for 5+ years, but has only been planted for the last 4 months, temp = 26°C. Water Parameters: pH ~ 7.8, Ammonia 0, Nitrite 0, Nitrates 25ppm, Phosphates >3ppm (based on calibrated Salifert test kits)
2. Filtration: 2x Fluval 404 filters with spray bars across the length of the tank, each filled with DIY coarse, medium and fine sponges, followed by filter floss and then 1.5kg of biohome ultimate and 500g of ceramic media. Total biofiltration = 4kg
3. Lighting and duration: 2 x 40W of T8 lighting for a continuous 9hr lighting period. In the past I tried upping this but that resulted in BBA on old dying leaves
4. Substrate: Inert Gravel
5. Co2 dosing or Non-dosing: Non dosing pressurised CO2 or liquid carbon
6. Fertilisers used + Ratios:
a. Daily Fert Dosing:
1.5ppm K (10.5ppm total per week), 0.8ppm Mg (5.6ppm total per week),
b. Weekly Fert Dosing: Micros to achieve 0.1ppm Fe with a mix equivalent to the APFUK chelated trace. I know I most likely have a iron deficiency because my tank pH is ~7.8, I have ordered Fe DTPA and Fe EDDHA to help with this and will dose 0.1ppm of each when it arrives
7. Water change regime: 30% weekly done with London Tap water which is quite hard, pH ~ 7.8, Ca++ 100ppm, Mg++ 5ppm.
8. Plant list: S. Repens, L. Sessiflora. Rotala Indica, Rotala Rotundifolia, Java Fern, Java Moss, Christmas Moss, Helanthium Tennullum, Dwarf Sag., Lobelia Cardinalis, Crypt Wendtii Brown, Anubias Barteri, Salvinia Natans
9. Inhabitants: 20 x Neon Tetra, 20 x guppies (various sizes), 7 x Ember Tetras, 6 x Glowlight Danios, 5 x Coral Red Platies, 1 x Safron Molly, 1 x long fin Bristlenose Pleco, 100+ x Red Cherry Shrimp, a few mini ramshorn snails.
10. Full tank shot: Posted along with some photos of the issues I am facing.

Please let me know if any further info/photos are needed, apologies for the slightly blurry images, the bow front makes it difficult to get good photos.
 

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