Eo you have a dry well that takes water from the washing machine and dishwasher? A typical family of four will use about 200-300 gallons of water per day. The generally guidelines, which I think are conservative, are 350 gallons per day for the first three bedrooms and 150 gallons per day for every additional bedroom. 

Your description of your system does not sound like it should fail. The only thing I might think of is during the cold snap, could the frost line extended into the drainfield and at least partially frozen it? This would slow water adsorption and allow it to accumulate in the lowest spot, the end of the line. 

It is not obvious that Septic Scrub would help your situation. I would need to have some additional information. 

The first suggestion would be to try to perk test the drainfield. This is done by digging a hole at the start of the lateral down to the top of the stone. Dig another one at the end of the lateral also. Then add water through your dosing tank. Add the recommended 350 gallons of water for the first three bedrooms and 150 gallons of water for each additional bedroom. Wait thirty minutes and measure the water level in each of the holes. Repeat the test after 24 hours. If the water level is higher the second day than the first, the field does not have the capacity to adsorb that amount of water in a 24 hour period. If you are sure that your water usage is only about 50 gallons per day (1600/30), then use this amount. This seems very low unless all non septic water is diverted into a drywell.

If you have an interest, please call me and discuss in further detail your situation.