Is nutrient temperature all that critical ?

[ChrisInTheTropics]

I've been planning a single shared reservoir for my hydro rigs, for a few reasons but mainly to keep the nutrient temperature under control as I live in the tropics and so, the 2 reservoirs I have that aren't buried in the ground in the shade can reach over 30 degrees, whereas the buried one ranges between 26 before sunrise to 28 at sunset - not a huge difference, and still too high, but the water from the deep well in the garden comes out at 26 so I'll not get it any cooler than that without refrigeration.

The thing is, my plants are growing pretty well it seems, I'm a beginner though, so don't have much to compare with.

I have 4 different NFT-ish setups fed from the two 'hot' reservoirs, with a variety of flow rates, nutrient depth etc. and have no cooler setup to compare with but I'm quite happy with how it's going.

The reservoir in the ground, which I've already dug involves laying lengthy pipes from the shady spot where I can bury it to where the plants are, which will need to cross the garden path and generally be a big ugly and in the way.

As such, I'm now thinking to stick with local reservoirs instead, and adding some galvanised steel wrapping to the tanks with an air-gap between steel and tank wall to help stave off the sun.

One worry is the increased possibility of root rot and other problems associated with higher temperatures, I'm using UV in the tanks to try to keep that down and will do a complete clean of each rig after each harvest, and will see how that goes.

I'm wondering, since the seeds I buy, and those I get free from local veg both come from around here, maybe the plants are already acclimatised to higher temperatures anyway, but I can't find any information about this, anyone have any ideas ?

 

[PitifulRoof75]

You're right that temps over 30C can raise root rot risk, especially in NFT systems. UV can help, but pairing it with good aeration and beneficial microbes is even better. As for galvanized steel, from what I know it can leak zinc, which may harm plants over time unless sealed properly.

 

[ChrisInTheTropics]

Thanks, 30C is about the upper limit, I've not seen it consistently above 29.something so far.

Happily no sign of root rot, all seems healthy, I guess it's a matter of not letting things slip with measuring/tuning the nutrient and a good cleanse after each harvest.

Yep, air stones and a good drop and splash from the return pipes should keep the O2 levels up, zero light gets into the tanks, not looked at beneficial microbes, but read here and there that they can be employed.

I'm tempted to put a strip of reflective tape along the sides of the long white 2.5" PVC tubes, well below the pot holes but where the sun shines, every little helps with getting the temperature down (while trying not to spend on electric chilling).

The steel is a good inch away from the outsides of the two big bins/tanks, I didn't want it touching so it can convect heat away in the gap on the inside too, like a shiny fence ringed around them both, it stands on the same flagstones but there's no contact with the nutrient or plants.

This is Indonesia, I bought the roll of steel from a local builder's merchant, so probably not sealed terribly well !

 

[HELYAB]

You're on the right track keeping an eye on temperatures. Cooler nutrient solution carries more dissolved oxygen and keeps opportunistic pathogens at bay, which is why most people aim around 20 to 22 °C. Once you get into the high twenties the risk of root rot goes up, but with strong aeration and clean systems plenty of growers in hot climates make it work. Burying or shading the tanks, wrapping them with reflective insulation and keeping them out of direct sun will slow heating. Running air stones and allowing a splash from the return pipes helps saturate the water with oxygen. Dropping frozen water bottles in during the hottest part of the day or using a small aquarium chiller are other tricks if you do see the reservoir creeping above 30. Local genetics and acclimated plants tend to be more tolerant of heat, so if your plants look happy and roots stay white there's probably no need to overhaul everything. Just keep an eye (and nose) on the reservoir and be ready to act if you notice slime or funky smells.

 

[ChrisInTheTropics]

Hi there, thanks for your detailed response. I'm a few months into it now and all seems to be going well, with 2 and a half rigs going we're self sufficient for 6 plants now (Bok Choi, Salada/Lettuce, Basil and three different Chinese spinaches), which is absolutely great, really pleased with how it's going

The reservoir of one is a pair of big plastic bins sitting directly on flagstones with shiny galvanised steel surrounds and lids with a good air gap between that and the bin walls and a few slots at the bottom to aid convection, which is keeping the temps down to about 28 degrees (not bad since it comes out of our well at about 26 and anything in direct sun easily passes 30 from 8am to 6pm !).

At that temperature all grows well, no rot as far as I can tell, no funny smells, great - so happily I don't need to bother with using ice blocks/bottles or incur the cost of electric refrigeration, both of which I was keen to avoid.

The 2 main setups are horizontal multi-pipe NFT rigs with UV lights and air stones running constantly, and the nutrient pumps running for 5 mins, then off for 10 mins; 20 mins an hour overall seems to be enough.

The other main rig has a polystyrene box as the reservoir which hangs around 28/29c but is a bit too small and I don't like the flimsiness of it, so that'll get a pair of bins like the other at some point.

The third/half rig is a mini-tower I bought in to try one out, it's a bit rubbish but good for an experiment and with our small garden that seems to the way to go, so I'm in the process of building a quad-2m-tower monster which will contain as many plants as the 2 main rigs combined but use half the floor area of either (and will be on castors !!); so we'll get a wider variety of greenery and grow herbs too, plus be able to supply my wife's parents and sister with produce

Now the base is built, I just have to drill/heat gun/glue about 212 8cm slices of pipe into the 4 towers... dreading that little task !!!