It seems amount of fluid transported is relatively low compared to resources.
I'm playing end game with Krastorio 2 and I'm having hard time keeping up with fluids (mostly sulfuric acid).
I can easily get 5-10 drones to keep single production cell going for normal goods, but need 40-50 for liquids. In my current example I need ~25K sulfuric acid per second and couldn't not get the drones to make it work even with 2 requester depots with each having 30 or 40 drones even though my supply depot for sulfuric acid was always full.
From my observation it looked like 2500 was delivered with each drone, so I would need 10 drones dropped off every second, which seems a lot.
I think fluid capacity should be higher than normal items.

The fluid capacity is the same as if you had the drones carrying barrels, I am not sure how else to make it make sense

Thanks for reply. Didn't realize that it's using barrels formula.

It makes a bit of sense for a fluid tanker to carry more than the same amount of volume of barrels, given barrels don't stack perfectly. Possibly not in game, dunno. I did notice something similar with requiring a lot more tankers than cargo trucks.

Just noticed a startup-up setting for "transport drone fluid capacity". Is that for vehicle fuel or can I use this to change how much fluid cargo they carry?

Yes, That setting is the "base stack" size for fluids.

25k acid per second ? a full tank or a full wagon per second ?
in vanilla that would require 200+ oil refineries, 650 chemplants (100+ of them for making the acid!), 150 miners and furnaces, and 70+ offshore pumps for the water alone ...
wouldn't that be a lot of acid even when transported by train, needing TEN(!) 3-6-3 trains per minute ?
a ratio of 1:10 (1 tanker wagon per second, or 10 drones per second) doesn't sound too unreasonable to me :-)

i would like to see a working base of those dimensions, when the acid alone is big as that ...
maybe Xterm would be interested in showing a base tour on YT ? :-)

Do you only have 1 fluid depot for acid?
I think it´s a throughput issue where your single fluid depot might be the bottleneck. Add more and I think your issues will be solved.

Your acid depot might be full all the time but I think the drones have some kind of reservation of the amount they will pickup while on their way (if I understand it right). So even if you have 25k stored you could also have 25 drones on their ways to pickup 1k (or 50 to pickup 500).
If you add more fluid depots you have more acid available for the drones to pickup.

This is with Krastorio mod, which makes all the resources quicker to produce with a ton of singularity beacons and chem labs are super fast (I think it's crafting speed of 8 or 10 and take more modules too).

The issue isn´t how fast you produce it´s how much you have available at any given time.

@Andrew: Lemlin already explained a possible limit caused by the mechanics of this mod.
and even without this limitation, vanilla would have problems transporting that much fluid that fast :

looking at the wiki and also following a link to the forums shows that a tankfull can directly be transferred from one tank through a pump to another tank in 2 seconds (best theoretical case, maybe even a hardcoded limit of 200 per tick) or 3 seconds. if the mod that you are using doesn't have faster pipes, tanks and pumps (would that be possible at all with the current fluid system in vanilla factorio?), that would be one possible bottleneck, and even more so if your setup has more pipes between the chemplants, tanks, fluid depots and pumps, down to maybe 1200 per second for a length of 18 pipe tiles or 9 underground pipes. (see also discussions how to provide enough water to big reactor setups that use chains of pumps instead of pipes).

since you want to transport 25k per second, that is three times as much as a vanilla setup can transport. and since slightly more than 100 vanilla chemplants are needed, even 20 times faster chemplants would require you to have 5 of them which causes longer transport pathes, even more so when you also have lots of beacons around each of them. do you have all pipes replaced by series of directly (without any pipes) connected pumps to improve the throughput ?

each single of these effects can easily reduce throughput to a third of what you want to achieve, and all effects combined will cause even less throughput. if you really use 5+ chemplants, you will probably do best with a separate buffer tank or a directly connected fluid depot for each of them, and only pumps and no pipes between them.

this should remove most of the vanilla bottlenecks, and by having 5 times as many fluid depots you also should be able to have 5 times more fluid reserved at the same time to be picked up during the next few seconds by lots of drones.