Peanut...throw in some beef dripping if you want REALLY good chips.
Throw it out (or compost it, or turn it in to biodiesel), as you won't be using it again in any reasonable period of time in a deep frier.
If the lid goes "gummy" you don't want to deep fry in it.
When my grandmother makes french fries she strains hers through a cheesecloth into a jar and uses it again within a one-week period. Twice is about it, after that it doesn't taste too great. And it's my understanding that you don't want to re-use it except with the same kind of food - otherwise the flavor of food #2 may be colored by food #1. Of course, I'm no expert.
When I deep fry stuff in mine I usually do a large amount of food (we in the southern US call it "a big mess" of food) and then throw the oil away. I only fry stuff every few months, so it wouldn't be wise to try and store it.
As far as temperature goes, I have a light on my deep fryer that indicates proper temp. When frying in a pan, I was always taught to take a very small bit of batter and throw it in the grease. If it doesn't start bubbling quite a lot as soon as it hits the oil it's not hot enough. It takes some practice, but you'll get the hang of regulating the temp. I'm sure there's a thermometer for this purpose, but I've never used one.
I'd recommend trying japanese 'panko' breadcrumbs on shrimp. It's easy to tell when they're done and they're one of the best fried foods IMO. They're exceptional drizzled with eel sauce, though it's a hard sauce to find.
I deep fry alot in the summer outside my pot holds about 3 gallons and use mainly canola oil. Best thing is to have a good pull out basket for the pot and a long dial reading temp and will fry 90% of everything at 350F. Will let oil settle overnight and strain back into original container and will fry 3 to 4 times with same oil. Biggest tip is to keep the oil right on the 350F mark throught the cooking do not over crowd the pot no matter what you fry. Peanut oil is over ratted and over priced IMO but to each his own.
PS Don't forget to salt when the food comes out of the oil that is the best time.
When deep frying if you want the batter to puff use very cold water almost freezing when mixing the batter.
Batter and Frying
A light batter is made of cold water and wheat flour. Eggs, baking soda or baking powder, starch, oil, and/or spices may also be added. Tempura batter is traditionally mixed in small batches using chopsticks for only a few seconds, leaving lumps in the mixture that, along with the cold batter temperature, result in the unique fluffy and crisp tempura structure when cooked. The batter is often kept cold by adding ice, or by placing the bowl inside a larger bowl with ice in it. Over-mixing the batter will result in production of wheat gluten, which causes the flour mixture to become chewy and dough-like when fried.
Specially formulated tempura flour is available in Japanese supermarkets. This is generally light (low-gluten) flour and occasionally contains leaveners such as baking powder.
Some varieties of tempura are dipped in a final coating, such as sesame seeds, before frying. Tempura generally does not use breadcrumbs in the coating. Generally fried foods which are dipped in breadcrumbs (panko) are considered to be furai (Japanese-invented faux western-style deep fried foods, such as tonkatsu or ebi Fried Prawn).
Thin slices or strips of vegetables or seafood are dipped in flour, then the batter, then briefly deep-fried in hot oil. Vegetable oil or canola oil are most common, however tempura was traditionally cooked using sesame oil. Many specialty shops still use sesame oil or tea seed oil, and it is thought that certain compounds in these oils help to produce light, crisp batter.
When cooking shellfish, squid, or hard-skinned watery vegetables such as bell pepper or eggplant, it is important to score the skin with a knife to prevent the ingredients from bursting during cooking. Failing to do so can lead to serious burns from splashing oil.
Oil temperature is generally between 160 and 180 degrees Celsius, depending on the ingredient. In order to preserve the natural flavour and texture of the ingredients, it is important not to overcook tempura. Cooking times range between a few seconds for delicate leaf vegetables, to several minutes for thick items or large kaki-age fritters.
It is important to scoop out the bits of batter (known as tenkasu) between batches of tempura, so they do not burn and leave a bad flavour in the oil. A small mesh scoop is used for this purpose. Tenkasu are often reserved as ingredients in other dishes or as a topping.