Once your plant gets big you’re going to need to top it up daily or as your water level goes down the ppm will go up. That’s one of the main reasons I use the tubs is for the extra volume and I only ever had to top up every 3 days. Pails are great for RDWC but as a stand-alone rez they are more hassle.
Also with each of the tub lids I made an extra hole for adding/removing water and using a 60cc syringe with tubing on the end could stick that in to draw out samples for pH and PPM testing or add small amounts of nutes to keep the ppm at the target range I wanted as the plants ate it up.
My procedure is to top up with RO or distilled water, allow 15 min or so for it to all mix up then do my testing. Before the pH perfect I would add my nutes using smaller syringes then allow some time before testing the pH as it would normally go up to 6.3 or so by top up. The nutes would generally bring the pH down a bit so you want to wait before adding any pH Down to get to 5.5 or so. It was so regular that I often skipped checking the pH and just dripped in a few drops of conc. sulphuric acid knowing that would bring it back down to around 5.5. Sometimes it might go as low as 5.1 but I just left it as I also knew it would begin rising right away. That swing between low and high makes sure that all nutrients are at some time at their optimum pH level and the plants will get lots during that time.
You actually have to be consistently out of range with pH before you start seeing problems with your plants. Mostly it’s the pH is too high which is common with soil/soilless growers using high PPM tap water but can happen to hydro growers using tap water who don’t change their nutes very often. Each time you water your plants with that they drink up the water but very little of the minerals that are in that water so they are left behind like the scale that builds up inside a kettle. Eventually they are blocking mostly micro-nutrients like iron and others so that problems show up first in the newest growth. Then serious flushing is the only solution to fix it.
Using RO water I often never change nutes even once during the whole grow. I tried it once using two tubs. One I changed 3 times during the grow and the other never at all. I couldn’t tell any difference in the growth or yields so said fuggit and didn’t bother changing at all after that. One change I try to do is right after the stretch then change to feeding Lucas Formula style. Zero Grow nutes and half as much Micro as Bloom so a 0-1-2 ratio of 3-part nutes in the GMB order.
Even using hard tap water there is no reason to change out weekly in the early stages of hydro. The small plants drink and eat very little so a good rule-of-thumb is to keep track of how much water you use to top up then once you’ve added back as much as your system holds it’s time for a fresh batch.
You will still need to add extra nutes as you go along and the plants get bigger so high ppm tap water makes that a lot harder to determine. Using pure water makes things a lot easier.
Have you checked your tap water for ppm? Even that only gives you some info so it’s best to get a water analysis report from your supplier to see exactly what all is in your water. Tap water can be high in minerals that are perfectly fine for drinking but can build up in your system and screw up your plants. It’s generally free and they can email you a copy on request. If they ask any questions just say you are raising fish or brewing beer and need to know but it’s really none of their damn business. 
A lot of problems can be avoided by using pure water in hydro and even soil/soilless growing. I never bother getting extra runoff in my potted plants to help reduce salts buildup as I try to not overfeed my plants so there is no extra salts to get rid of. Hard tap water adds in all sorts of extra salts that cause problems.
