Mixing Larger Qty my PPM is off

[Pondracer]

If I run the amounts in the feed chart and mix 1 gallon or 5 gallon batches everything is fine and I hit the target PPM. Once I switch up to 60 gallons or even 45 gallons the PPM reading is way off to the low side. All batches are mixed with RO-DI at 0ppm. Some of these amounts are almost double the recommended per gallon dosage for a 60 gallon batch. I usually begin mixing the SI at 40 gallons with the PH Down to get the PH close to normal. Dump another 5 gallons of water in at 1 hour to bring it to 45 and do a full mix for a few minutes. Then I mix in the order below. After that I take a PPM reading and add water as needed to hit ~600 ppm. I just reduced some amounts and started week 5 of flower using the chart below. I wasn't even able to add water after the initial mix because I was already too low at 484 ppm. This is typical. To hit the right numbers at a full 60 gallons requires me to use double the recommended amounts.

GH Armor SI: 90 ml
Cal-Mag: 120 ml
Jackpot Supplement: 60 ml
GH Flora Micro: 200 ml
GH Flora Gro: 50 ml
GH Flora Bloom: 275 ml
GH Koolbloom: 140 ml
BioAg Ful-Power: 500 ml
Yucca Wet: 250 ml
Rapid Start: 60 ml
H2O2: 250 ml

45 gallon mix / 484 PPM