GSA and plant deterioration - increase macro dose or supplement PO4?

[Tom101]

Thanks Darrel - I've actually got some Potassium, Magnesium and Iron lying around so can certainly try those.

 

[dw1305]

Hi all,

I've actually got some Potassium, Magnesium and Iron lying around so can certainly try those.

It isn't going to do any harm.

With the potassium (K) and magnesium (Mg) you get a pretty quick greening response, if either of those was Liebig's limiting nutrient. The same applies for nitrogen (N) and phosphorus (P). The are all mobile within the plant and it can shuffle them to the newest photosynthetic tissue.

It is a bit different for iron (Fe), it very quickly goes out of solution and we need a chelator to ensure Fe++(+) ion availability, and also it isn't mobile within the plant, so it is only new leaves, that grow after iron becomes available again, that are greener.

cheers Darrel

 

[Tom101]

Good to know - any specific dosages recommended? (70ltr tank, no co2)

 

[John q]

Distance from the bottom of the light housing to the top of the substrate is approx 31.5cm.

Cheers Tom, shallow tank, that makes a bit more sense now.

Going to add a big caveat here: Trying to guesstimate par readings isn't very accurate, even if you have known calibrated par meter readings from one light fitting the chances are the next one will be slightly different.
The figures I'm going to guesstimate are based on manufacturer provided figures, which aren't always accurate and hobbyist provided numbers.

Based on a few fluval light fixtures I think we can hazard a guess and come up with a ballpark figure regards how much par you have at the substrate of your tank; incidently, if you still have the original box for the light it will give you various par readings on there.

Based on what par numbers I know for the 59w plant 3, 33w aquasky 2 and 16w aquasky 2 ~ I reckon at 100% power your light will produce between 58 ~ 66 par at a depth of 12", that's within a 3" band directly underneath it. This assumes no shading.
Assuming this number is remotely accurate (?) It then leaves us with the question "what will your light at 16% provide." Well.. if par drop off is linear to percentage reduction (I've no idea if it is) it would give us 62 ÷ 100 x 16 = 9.92 par.

Turn up the <"intensity a bit"> and that will at least take low light away from our possible causes of poor plant growth.

If my long winded guesstimate above is anything like accurate (it might not be) then this could well be correct. It's very unusual I'd suggest doing this but if there is only 10 par at the substrate then this will be getting pretty close to the plants light compensation point, in layman's terms the amount of light they need to actively grow.
If you did follow this route I'd only increase the light a bit, say upto 20% and see if there's any improvement.


Fertiliser wise I personally think you're adding enough other than phosphate. If you look at what numbers you're adding some of these nutrients are at 50~75% ei levels. This in my opinion is more than enough in a low light, low tech tank.

Your phosphate levels are currently at 1.8 ppm po4, I'd raise this to 3 ~4 ppm and see if the new growth with increased light is free of gsa. We don't know why increased phosphate reduces gsa but a number of us have managed to keep it at bay by raising the levels.

I guess its all about trail and error Tom, I don't claim to have all the answers, just lots of best guesses. 😀

 

[Tom101]

Thanks @John q some great info there. I'll get some Phosphate purchased and crack on with the above. Really appreciate the insights!