Looking to understand better how I am fertilising my 45 litre planted tank. There's no problem, actually everything is going rather nicely at the moment (touch driftwood!), but this is more by luck than a complete understanding of what I'm doing. Would appreciate any insights, guidance, links to useful reading material, etc, please!
Tank is 45 litre, Amazonia substrate, Kessil A360X light, pressurised CO2, light fish load (5 zebra danio, 6 cardinal tetra, 2 nerites, 4 amano shrimp), external Fluval 207 canister filter, established about 6 months ago and all seems pretty happy and stable.
Plants are all fairly low demanding I think:
- lots of Christmas moss blanketing driftwood
- java ferns
- eliocharis pusilla grass
- floating salvinia currently covering half tank surface
Heavily planted in terms of minimal substrate visible, but no demanding stem plants etc of any sort.
My goal is to have a lush green tank where the plants are all healthy, but that doesn't need a massive amount of constant plant trimming and maintenance. This is what I currently have, algae in retreat for now, all looking great, tank seems in balance and taking care of itself without too much interference, critters happy, kids love it, enough maintenance required for relaxed pottering after kids asleep but not too demanding
I fertilise with full Seachem range except for Excel and Advance (so Flourish, Trace, N, P, K and iron) based on Seachem's suggested weekly dosing schedule. Tank started off with soft tap water, now using RO water, always remineralised to 7GH with Equilibrium. Initially I assumed that Seachem's dosing must be based on a heavily planted tank with demanding plants so I dosed at 50% of their recommendations thinking this might still be too much. But whenever I tested the tank water, nitrate and phosphate were both zero.
So I upped dosing to 100% recommended dose. Plants maybe looked a bit better but still zero nitrate and phosphorous measured in the tank water. I test with API liquid test kits, and I've checked that they are working properly by making up reference solutions with respective fert's in plain RO water. I have now upped the dosing to 200% of Seachems recommended "beginner" dose for N, P and K (still at 100% for Flouorish, Trace and iron), but still no nitrate or phosphate at the end of the week before a water change.
I don't see any sign of deficiency, but I'm also aware that apart from the blaringly obvious, I'm not at all experienced at this! All the plants are lush green, which is what I wanted. So everything seems good and I don't think I need to change anything. But, I have these questions:
1) Should there not be some leftover nitrate and phosphate in the water column at the end of the week before I do a water change? Occasionally I might see a hint of nitrate, but usually zero and never the slightest sign of phosphate (although the API test kit doesn't have much resolution at the low end).
2) If there is no trace of nitrate and phosphate in the water column, does this mean that I am limiting the plants? (Actually I don't want them to grow any faster because I don't want to have to do more maintenance and everything looks good as is, but just to understand what's going on).
3) I probably don't need to dose iron (no red leaf or stem plants), but thought might as well buy in to the whole Seachem lineup from day one...
4) I don't have a potassium test kit so have no idea of the level in the tank. I dose nitrogen, phosphorous and potassium all at 200% of the Seachem recommended beginners dose assuming that the strength of the 3 products already takes into account the typical ratio in which they are required by plants. So I'm assuming that there is also no potassium in the water column by the end of the week - is that a safe / sensible assumption to make?
5) If I wanted maximum plant growth (which I don't!), would I increase the NPK dosing to 300%, 400%, 500% of Seachem's beginner dose until I consistently see leftover nutrients in the water column just before the water change?
6) It seems that the salvinia I have floating on the surface really sucks up nitrates (other fert's too?) from the water. Is this why I never seem to see any nitrate or phosphate in the tests? This was the plant that I noticed the biggest increase in growth in when I upped the NPK dosing from 100 to 200%. I guess it sucks up whatever the water column offers, but then am I limiting the other plants if the floating salvinia is stealing everything? (I use this tank to grow it for my other shrimp tanks where the critters like to munch holes in it and where it doesn't grow so lushly due to lack of light, CO2 and lower fert's).
Ok, so hopefully that kind of explains where I'm at in my understanding and learning. Have I got anything wrong, misunderstood or plain missed something? All guidance gratefully received!
Just to note:
- I want to stick with Seachem fert's line due to ease of sourcing here in Singapore, and my tanks are small so cost is not an issue as I don't use that much
- I have no interest in mixing my own fert's and can't easily access dry powders here. I'm happy for Mr Seachem to do all that and sell it to me in a nice bottle.
- IE dosing doesn't appeal to the engineer in me that likes measurement, precision and exactness. Just adding way more than the plants will ever never makes sense when you want to maximise growth, but I would prefer to learn enough to be able to dose what my plants actually need and be able to maybe hold them back slightly at peak health to minimise maintenance