I text out a roll call to my techs once a week or every other week to see what chems levels are on the truck and at the shop for the ones I want to order in bulk. My techs have gotten really good at letting me know when tubs are getting low so I am not scrambling to refill. As far as parts, we are still at the level of order as you go / get approval.

We utilize the shopping list on skimmer. When the guys grab their trucks from the shop every morning they stock up at the shop. We keep a pretty good amount of chemicals etc. at the shop. Then I will usually take a look at inventory daily and add things to the shopping list as needed and order them when I order my stock orders. Its old school but it works. 

From a systems standpoint, QBO is a decent option if you are using it already.  It’s not perfect, but it’s a solid entry-level inventory management system, particularly if you’re managing inventory manually right now.  You’ll need the Plus or Advanced version of QBO.  If you don’t have it, the upgrade is easy and affordable.  Like with any robust WMS/IMS, you’ll need to do routine manual counts to keep the inventory in control, but QBO makes that simple by offering pre-configured count sheets.  I deployed the QBO option with our pool and spa company and have been happy with the results.  It’s easily paid for itself, and we rarely (if ever), run out of critical items.  Beyond that, we no longer overstock anything, which historically was a significant issue for this company.  A little knowledge of inventory control, min/max programming, and a solid re-ordering/restocking process and you will be good to go.  Hope that helps.