Vtyjkyuk

I've ridden a fixed gear bike for years now, but I've only just questioned if I have been doing something wrong when adjusting the chain.
You see, I have to tension the chain (pulling the rear wheel back) every now and then, roughly once a month because the chain becomes very loose with regular riding.
At first I tried to keep the chain as tight as possible, so that there's pretty much no latency in the pedals when the bike is stationary (don't know if this is the correct expression) but then I read somewhere that doing this with fixed gear bikes can damage the drivetrain, and you should actually have a little latency and thus a slightly loose chain.

In short, my questions are:
Is it normal that I have to tighten the chain probably at least once a month because it gets too loose with casual riding, no more than a 100 miles per week?

Is it correct that with fixie you shouldn't keep the chain too tight because it can ruin the drivetrain?

There are already some exhaustive answers in this thread, I won't be repeating those.

To shortly answer your questions:

• 
  no, I don't think so. I've ridden a fixie myself and after about 500km I've loosened my chain because of the reason given in your second question. Since then it's been more than 500km again, no chain tension adjustment needed.


• 
  yes, you're correct about damaging the drivetrain, stretching the chain and putting excessive (and uneven) stress on the bearings in the bottom bracket and the rear axle.

If applying a correct torque to the nuts of the rear axle doesn't help perhaps you should resort to one of the following items mentioned in this answer: https://bicycles.stackexchange.com/a/56603/34697?

Those are:

• serrated/star washer
  




• chain tension adjuster, is only to be applied to the rear-facing dropouts.
  

Is it correct that with fixie you shouldn't keep the chain too tight because it can ruin the drivetrain?

That is mostly correct. Given that the circularity of the chainring, bearings and rear sprocket are never ideal, there will be a position through a full crank's rotation when the chain is the most tight, and a position where it is the most loose. It is recommended to find the tightest spot and tune the chain tension to be just right in it. Then, just in case, you can find the loosest spot and make sure the chain won't hop off the teeth if shaken in the second position.

Overtightening a chain would not give performance benefits while simultaneously it would start pressing both chain and chainring excessively, not benefiting their wear life.

Is it normal that I have to tighten the chain probably at least once a month because it gets too loose with casual riding, no more than a 100 miles per week?

If it is not the rear wheel axle sliding forward because of a low torque on its axles or because of bad nut design/quality, then it is the chain. You would have noticed the axle sliding because the rear wheel would become misaligned in the rear dropouts and the tire would start rubbing one of the rear chainstays.

It is possible that a chain of poor quality would wear faster than desired, effectively "stretching" itself and thus becoming loose on the drivetrain's teeth over time. I've read reports that so called half-link chains used in BMX are quite prone to it. Try using a better, possibly more expensive chain.

Again, if the chain seems "loose" to your taste but you cannot throw it off the drivetrain's teeth by hand, it is unlikely it will come off during riding. In that case, let it be for a while.

And again, do not forget about regular maintenance of the chain, that is, replacing it after it has worn and become longer by 0.75% of its original length.

The rear wheel should not simply be pulled back so that the chain is taught. Doing so would accelerate wear.

When properly tensioned you should be able to move the chain about 12mm (0.5 inch) up or down about halfway between sprocket and chainring.

To rule out wheel movement, you could invest in a set of chain tensioners that fit in the dropouts. These will also make setting chain tension and wheel alignment easier.

As usual, Park Took has a great video on single speed chain replacement and tensioning:

Other answers have already covered the part about why chain should not be too tight, so I will answer only about chain wearing.

It is not normal, but not completely unheard of. The worst singlespeed chain I have had wore out in about 1000 km and had to be tightened halfway during long rides. It was marketed as rust proof, I guess the idea is that the chain would wear out before it had time to rust. It was not because the wheel was moving in dropouts, and switching to a different brand solved the problem.