multiple water tanks ?

[IamPixel]

is it advisable to use more than 1 tank. in 15 large planter box and 15 planter box ?

[tevrarain]

You mean the fertilizer tanks? I'd be interested to know how that works as well.

[Ginkaku]

This looks like a job for SCIENCE!

[Talyn]

I use 1 tank for about 240 small planters - with Ack's help of course.

The Irrigation Tower[mytimeatportia.fandom.com] can hold 20 units of Fertilizer; Small Planters[mytimeatportia.fandom.com] can hold 3 Fertilizers; Large Planters[mytimeatportia.fandom.com] can hold 6 Fertilizers.

[worstcase11]

I was using two irrigation tanks in my last playthrough, since I set up a rather large farming area. It is not really neccessary as a tank can be refilled as often as needed a day, but I don't like the idea of my giant vegetables being cut off from fertiliter for too long - they have very high fertilizer level standards.
Fertilizer goes down and up (when refilled) equally on both tanks btw.

[kwsapphire]

TL;DR: Using more tanks gives you a bigger reservoir so you have to check & refill them less often.

If you have 15 large and 15 small planters, your fertilizer needs will be determined by what you actually planted. If each of those plants only need 1 fertilizer per day, you'd only need 1 tower and need to refill it once per day. (Each tower holds 30 fertilizer.) Obviously if your plants eat more than one fertilizer per day, you'll need to refill the tower more often.

I currently have 3 irrigation towers, and will buy a 4th after I buy the final land expansion & finish surrounding my property with apple trees. This is because I already have about 50 trees and like.. 20-ish small planters (with more planned). I could get away with refilling the tanks once per day, but I refill them at least twice per day - once first thing in the morning and again in the evening. Once I plant my next Giant Vegetable in the spring, I'll have to be even more diligent about it.

[Bobucles]

TL;DR: Using more tanks gives you a bigger reservoir so you have to check & refill them less often.

Nailed it.
Every plant can survive at least a day without fertilizer. So a single tank can take care of it. Just beware that if it runs dry, it may need to be refilled multiple times to replenish the field.

Fertilizer is largely an all or nothing deal. Plants consume fertilizer all the time, but they only gain a happiness bonus if the fertilizer stays rich enough. Scraping along just barely enough to keep them unhappy is the worst position to be in, you spend the money but gain nothing from it. The fertilizer tank makes plant maintenance easy. It will top everything off so you only have to fill a single thing.