EA performance in tester vs live

[Plamen Zhivkov Kozhuharov]

Hi,

First of all, apologies if this has been discussed before. 

I have optimised an EA (with GBPUSD on M30 and H1) which now produces absurdly profitable results in the MT4 strategy tester using recent data. The problem is, it’s been on my demo account for nearly a week now and has almost melted the account.

I would be grateful if anyone could make a list of possible reasons as to why this may be happening so I can investigate these. 

Any input along those lines would be greatly appreciated. Thank you.

[Plamen Zhivkov Kozhuharov]

I’ve discovered that when in offline mode, the tester produces a terrible result which more or less reminds me of the demo results. Any thoughts?